LRC 12.2.1 Metadata Status resets itself

System:
Lightroom Classic 12.2.1

Mac M1

MacOS Monterey 12.6

I Imported some photos from another catalog yesterday and did some updates to the keywords. The Metadata Status was set to "Has been changed" as expoected. I then tried to save the metadata. For some pictures (the minority), Metadata Status changed to "Up to-date" and stayed there as expoected. For the majority however it changed to "Up to-date" before automatically beeing changed back to "Has been changed". I tried a few photos seperatly again and it still happens the same.
I always save the metadata in the files itself, without a sidecar xmp file. I checked with Photo Mechanic and the Metadata is written to the files correctly, when I save it manually.The files are JPEGs, which always seem to work correctly.
The majority were DNG files that were converted by Lightroom Classic (some years ago) from Canon 5D Mark III, Canon 7D and Fuji X100 Raw files. I validated a few of the DNG files in Lightroom and they were shown as being ok. The majority of the DNG files behave incorrectly, but some of the DNG files behave correctly. The correct and incorrect DNG file are locaated in the same directories.

This is the first time that happend to me and all older files in the same cataloge seem to work ok.
Does anyon has any idea, what is going wrong here?