Hey Marcel, I'm impressed you noticed this. Your question was discussed internally by some Liferay Engineers, and it looks like it's working as expected. Here's why: 

Editing an article creates a new version. This new version is indexed alongside the first one. TF-IDF (Term Frequency-Inverse Document Frequency) scoring dictates that having additional indexed content that closely (in your case, identically) matches the original copy will cause the significance of matching terms in the document corpus to get lower, and thus a lower score results. In this case, it's the IDF part that's lowering the score, because now the search term appears in more documents in the index. The match is essentially less unique and thus deemed less significant.

Updated to add:

If you'd like to offset the score-lowring effect of article versions you could try to boost the score of some documents using the Custom Filter widget. 

For example, Web Content articles seem to have a field that indicates a version as the latest version of the article. The field is called head. It looks like it's true for the latest version, and false for a past version. See the Custom Filter documentation for inspiration.

In addition to the Custom Filter, some helpful tools in this quest: 

Search Insights widget
Search Results widget, with View in Document Form enabled

To Look at the raw indexed content (including older versions of the article) hit the Elasticsearch API directly. For example, in my running 7.4 local bundle (running the Sidecar Elasticsearch server) I used the following URL to look at all indexed web content:

http://localhost:9201/liferay-20099/_search?q=entryClassName:"com.liferay.journal.model.JournalArticle"&pretty=true
 

I hope that helps.