Git history does not merged

Hello everyone.

Have a main master branch. Create featured branch vesnin-dev, make some commits in branch.
After work completed, create merge request wia Web UI in Gitlab. MR forms show my commits and changes. Ok Merge it… All fine but history look like on screen on left side.

Trying create MR again, forms show my commits and no changes (0 files changed). WTF?
Again press Merge - merge completed and closed. History does not changed.

Trying make another test branch - no problem (pink “loops” on left side).
Ok, com back to my broken branch vesnin-dev, make local merge via command line to master - history look as it should be.

Pls, can you explain me why gitlab history looked wrong when merged via web ui?