Here are the gogoshell outputs for the commands you suggested:

g! lb -s | grep "com.liferay.login.web"

 1242|Active     |   15|com.liferay.login.web (5.0.26)|5.0.26
 1271|Active     |   10|com.liferay.login.web.api (1.0.6)|1.0.6
true

 g! headers 1242

Bundle headers:
 Bnd-LastModified = 1611587464297
 Bundle-ManifestVersion = 2
 Bundle-Name = Liferay Login Web
 Bundle-SymbolicName = com.liferay.login.web
 Bundle-Vendor = Liferay, Inc.
 Bundle-Version = 5.0.26
 Created-By = 1.8.0_221 (Oracle Corporation)
 Import-Package = aQute.bnd.annotation.metatype,com.liferay.captcha.configuration;version="[1.0,2)",com.liferay.captcha.util;version="[1.1,2)",com.liferay.expando.kernel.model;version="[3.3,4)",com.liferay.exportimport.kernel.lar;version="[3.3,4)",com.liferay.osgi.service.tracker.collections.list;version="[2.0,3)",com.liferay.petra.content;version="[1.0,2)",com.liferay.petra.sql.dsl.query;version="[1.0,2)",com.liferay.petra.string;version="[1.4,2)",com.liferay.portal.configuration.metatype.annotations,com.liferay.portal.kernel.annotation;version="[7.0,8)",com.liferay.portal.kernel.bean;version="[8.0,9)",com.liferay.portal.kernel.captcha;version="[7.0,8)",com.liferay.portal.kernel.dao.orm;version="[9.7,10)",com.liferay.portal.kernel.exception;version="[9.3,10)",com.liferay.portal.kernel.json;version="[8.7,9)",com.liferay.portal.kernel.language;version="[8.3,9)",com.liferay.portal.kernel.log;version="[7.0,8)",com.liferay.portal.kernel.model;version="[5.6,6)",com.liferay.portal.kernel.module.configuration;version="[2.0,3)",com.liferay.portal.kernel.portlet;version="[10.2,11)",com.liferay.portal.kernel.portlet.bridges.mvc;version="[3.0,4)",com.liferay.portal.kernel.resource.bundle;version="[1.0,2)",com.liferay.portal.kernel.search;version="[9.3,10)",com.liferay.portal.kernel.security.auth;version="[2.4,3)",com.liferay.portal.kernel.security.auth.session;version="[1.0,2)",com.liferay.portal.kernel.service;version="[4.8,5)",com.liferay.portal.kernel.servlet;version="[8.4,9)",com.liferay.portal.kernel.settings;version="[3.1,4)",com.liferay.portal.kernel.theme;version="[3.1,4)",com.liferay.portal.kernel.upgrade;version="[8.5,9)",com.liferay.portal.kernel.upload;version="[8.1,9)",com.liferay.portal.kernel.util;version="[10.16,11)",com.liferay.portal.kernel.workflow;version="[9.5,10)",com.liferay.portal.kernel.xml;version="[7.0,8)",com.liferay.portal.security.auth;version="[2.0,3)",com.liferay.portal.upgrade.registry;version="[3.0,4)",com.liferay.portal.util;version="[4.12,5)",com.liferay.taglib.include;version="[1.0,2)",com.liferay.taglib.portlet;version="[7.3,8)",com.liferay.taglib.ui;version="[9.1,10)",javax.portlet,javax.servlet,javax.servlet.http,javax.servlet.jsp;version="[2.3,3)",org.osgi.framework;version="[1.8,2)",javax.net.ssl
 Javac-Debug = on
 Javac-Deprecation = off
 Javac-Encoding = UTF-8
 Liferay-Releng-App-Title = Liferay Login
 Liferay-Releng-Bundle = true
 Liferay-Releng-Category = Utility
 Liferay-Releng-Deprecated = false
 Liferay-Releng-Fix-Delivery-Method = core
 Liferay-Releng-Labs = false
 Liferay-Releng-Marketplace = true
 Liferay-Releng-Portal-Required = true
 Liferay-Releng-Public = false
 Liferay-Releng-Restart-Required = true
 Liferay-Releng-Suite = foundation
 Liferay-Releng-Suite-Description = Apps and Features: System Settings, Web Content Editors, Web Content Template Languages, Theme Tools, Mobile Device Rules, Facebook Authentication, LDAP Authentication, NTLM Authentication, OpenID Authentication, OpenSSO Authentication, Remote Authentication (AuthVerifiers), SSO-based Authentication, Token-based Authentication, Portal Scripting, Elasticsearch Support, Solr Support, Documents and Media Store Implementations, and more.<br /><br />The Foundation suite provides applications and features that extend the functionality provided by Liferay's core. Much of the functionality that belonged to Liferay's core prior to Liferay 7 has been extracted into the modules of the Foundation suite. The authentication modules provide a variety of mechanisms for allowing users and remote applications to authenticate to Liferay. The LDAP Authentication module allows administrators to establish connections to one or more LDAP directories from which users can be imported or exported. The SSO modules allow users to authenticate to Liferay using a variety of single-sign on solutions. The Token-based Authentication module allows users or remote applications to authenticate to Liferay without a password. The Scripting modules allow scripts to be written to invoke Liferay's API in several languages including Groovy, BeanShell, Python, Ruby, and JavaScript.<br /><br />This suite is available in the Liferay bundle.
 Liferay-Releng-Suite-Title = Liferay Foundation
 Liferay-Releng-Support-Url = http://www.liferay.com
 Liferay-Releng-Supported = true
 Manifest-Version = 1.0
 Private-Package = com.liferay.login.web.internal.portlet,com.liferay.login.web.internal.portlet.action,com.liferay.login.web.internal.portlet.util,com.liferay.login.web.internal.servlet.taglib.include,com.liferay.login.web.internal.upgrade,com.liferay.login.web.internal.upgrade.v1_0_0,content,resource-actions
 Provide-Capability = osgi.service;objectClass:List<String>="com.liferay.portal.kernel.portlet.ConfigurationAction";uses:="com.liferay.portal.kernel.portlet",osgi.service;objectClass:List<String>="com.liferay.portal.kernel.portlet.bridges.mvc.MVCActionCommand";uses:="com.liferay.portal.kernel.portlet.bridges.mvc",osgi.service;objectClass:List<String>="com.liferay.portal.kernel.portlet.bridges.mvc.MVCRenderCommand";uses:="com.liferay.portal.kernel.portlet.bridges.mvc",osgi.service;objectClass:List<String>="com.liferay.portal.upgrade.registry.UpgradeStepRegistrator";uses:="com.liferay.portal.upgrade.registry",osgi.service;objectClass:List<String>="com.liferay.taglib.include.PageInclude";uses:="com.liferay.taglib.include",osgi.service;objectClass:List<String>="javax.portlet.Portlet";uses:="javax.portlet",liferay.resource.bundle;bundle.symbolic.name="com.liferay.login.web";resource.bundle.base.name="content.Language"
 Require-Capability = osgi.extender;filter:="(&(osgi.extender=jsp.taglib)(uri=http://java.sun.com/portlet_2_0))",osgi.extender;filter:="(&(osgi.extender=jsp.taglib)(uri=http://liferay.com/tld/aui))",osgi.extender;filter:="(&(osgi.extender=jsp.taglib)(uri=http://liferay.com/tld/captcha))",osgi.extender;filter:="(&(osgi.extender=jsp.taglib)(uri=http://liferay.com/tld/clay))",osgi.extender;filter:="(&(osgi.extender=jsp.taglib)(uri=http://liferay.com/tld/frontend))",osgi.extender;filter:="(&(osgi.extender=jsp.taglib)(uri=http://liferay.com/tld/portlet))",osgi.extender;filter:="(&(osgi.extender=jsp.taglib)(uri=http://liferay.com/tld/theme))",osgi.extender;filter:="(&(osgi.extender=jsp.taglib)(uri=http://liferay.com/tld/ui))",osgi.extender;filter:="(&(osgi.extender=jsp.taglib)(uri=http://liferay.com/tld/util))",osgi.extender;filter:="(&(osgi.extender=osgi.component)(version>=1.3.0)(!(version>=2.0.0)))",osgi.service;filter:="(objectClass=com.liferay.portal.kernel.model.Release)";effective:=active,osgi.service;filter:="(objectClass=com.liferay.portal.kernel.module.configuration.ConfigurationProvider)";effective:=active,osgi.service;filter:="(objectClass=com.liferay.portal.kernel.security.auth.session.AuthenticatedSessionManager)";effective:=active,osgi.service;filter:="(objectClass=com.liferay.portal.kernel.service.LayoutLocalService)";effective:=active,osgi.service;filter:="(objectClass=com.liferay.portal.kernel.service.ListTypeLocalService)";effective:=active,osgi.service;filter:="(objectClass=com.liferay.portal.kernel.service.UserLocalService)";effective:=active,osgi.service;filter:="(objectClass=com.liferay.portal.kernel.service.UserService)";effective:=active,osgi.service;filter:="(objectClass=com.liferay.portal.kernel.util.Http)";effective:=active,osgi.service;filter:="(objectClass=com.liferay.portal.kernel.util.Portal)";effective:=active,osgi.contract;osgi.contract=JavaServlet;filter:="(&(osgi.contract=JavaServlet)(version=3.1.0))",osgi.contract;osgi.contract=JavaPortlet;filter:="(&(osgi.contract=JavaPortlet)(version=3.0.0))",osgi.ee;filter:="(&(osgi.ee=JavaSE)(version=1.8))"
 Service-Component = OSGI-INF/com.liferay.login.web.internal.portlet.FastLoginPortlet.xml,OSGI-INF/com.liferay.login.web.internal.portlet.LoginPortlet.xml,OSGI-INF/com.liferay.login.web.internal.portlet.action.CreateAccountMVCActionCommand.xml,OSGI-INF/com.liferay.login.web.internal.portlet.action.CreateAccountMVCRenderCommand.xml,OSGI-INF/com.liferay.login.web.internal.portlet.action.CreateAnonymousAccountMVCActionCommand.xml,OSGI-INF/com.liferay.login.web.internal.portlet.action.CreateAnonymousAccountMVCRenderCommand.xml,OSGI-INF/com.liferay.login.web.internal.portlet.action.ForgotPasswordMVCActionCommand.xml,OSGI-INF/com.liferay.login.web.internal.portlet.action.ForgotPasswordMVCRenderCommand.xml,OSGI-INF/com.liferay.login.web.internal.portlet.action.LoginConfigurationActionImpl.xml,OSGI-INF/com.liferay.login.web.internal.portlet.action.LoginMVCActionCommand.xml,OSGI-INF/com.liferay.login.web.internal.portlet.action.LoginMVCRenderCommand.xml,OSGI-INF/com.liferay.login.web.internal.portlet.action.LoginRedirectMVCRenderCommand.xml,OSGI-INF/com.liferay.login.web.internal.servlet.taglib.include.AnonymousNavigationPrePageInclude.xml,OSGI-INF/com.liferay.login.web.internal.servlet.taglib.include.CreateAccountNavigationPostPageInclude.xml,OSGI-INF/com.liferay.login.web.internal.servlet.taglib.include.ForgetPasswordNavigationPostPageInclude.xml,OSGI-INF/com.liferay.login.web.internal.servlet.taglib.include.SignInNavigationPrePageInclude.xml,OSGI-INF/com.liferay.login.web.internal.upgrade.LoginWebUpgrade.xml
 Tool = Bnd-4.3.0.201909301554
 Web-ContextPath = /login-web

g! headers 1242 | grep "Bundle-Version"

 Bundle-Version = 5.0.26
true

Now this is the gogoshell output for my own created Liferay Module Project Fragment test-login-fragment:

g! lb 

...
1369|Installed  |   15|test-login-fragment (1.0.0)|1.0.0

g! diag 1369

test.login.fragment [1369]
  Unresolved requirement: Fragment-Host: com.liferay.login.web; bundle-version="5.0.26"

g! headers 1369 | grep "Bundle-Version"

 Bundle-Version = 1.0.0
 Portal-Bundle-Version = 7.3.6

I cant see the error here. I have  Bundle-Version = 5.0.26 for "com.liferay.login.web" installed. 
And again: It works if I deploy through eclipse servers view add and remove. 
It does not work if I deploy via gradle deploy / dropping the built .jar file into the deploy folder.

That is really perplexing.

What if you drop the fragment right into osgi/modules?

Also, what happens if you refresh the host after deploying the fragment?

refresh 1242

There should be a way to see what's attached to the host module as well, via Gogo shell. I'll look into that.

Thanks for your reply, I could test you suggestions today and the refresh of the host module helps. 

For some reason this refresh is not triggered automatically. A normal gogo shell 'refresh' command does not help. I have to refresh the host module explicit. 

In the past I didnt have to do that...

How do I prevent this?
What if this happens in production?

 

I can confirm that I have created a fragment for com.liferay.login.web on 7.3 DXP patched up to FP1, and using a Jar created by ./gradlew build, the fragment remains in the installed state and does not attach to the host module unless I manually refresh the host in the Gogo shell. I'll see if I can poke someone internally who might be able to confirm a bug or else tell us whether somethiong changed intentionally.

Thank you for the answer and thank you for 

I'll see if I can poke someone internally who might be able to confirm a bug or else tell us whether somethiong changed intentionally.

 I appreciate it!