I just experienced a similar thing. I lost all tags that I had put for my tasks for the past two months! For context, I have one task called "Work", and rely on the tags to categorize what I am working on. This way, I can see what work I have been doing. A tag is usually a project and a type of task. Over time, this has helped me see where I put my time. But now, Timo, I have lost this wealth of data out of nowhere.
Let me also add that I just upgraded my Mac OS from 15.2.xxx to 15.4. That's when I noticed this. But I have tags on my tasks from 3 months back and beyond. Only these past two months have completely disappeared.
Thank you!
OS Version: Mac OS X 15.4
App Version: 2.11.28