JabRef 5.2--2020-12-03--a06f2e0
Linux 4.12.14-lp151.28.83-default amd64
Java 15.0.1

• Mandatory: I have tested the latest development version from http://builds.jabref.org/master/ and the problem persists.

Steps to reproduce the behavior:

1. Open a(n empty) shared database.
2. Add some entries to "All entries". Works fine.
3. Add a subgroup S1.
4. Add an entry to subgroup S1. Two entries will appear in entry list. Both are somehow "linked" to each other.
5. Change one of the two new entries in the subgroup. The entry conflict window (like with concurrent access) pops up. So it seems like both entries are actually the same entry.
6. Reload the database. Previously added Entries under "All entries" disappeared. Phantom entries disappeared as well.

It seems like a problem with proper synchronization. I had encountered a similar problem when I interchanged lines 83 and 84 in DBMSSynchronizer.java:
line 83: synchronizeLocalDatabase();
line 84: dbmsProcessor.insertEntries(event.getBibEntries());

Maybe there lies a part of the problem?

Paste an excerpt of your log file here