Problem with one termbase – urgent

I'm working on a project with 4 termbases and the default one suddenly stopped working. I successfully added several terms this morning, and then when I wanted to add other terms later, I always received an error message telling me that the modifications could not be made because there was a duplication risk in the index fields?! Now I don't even see the added terms in the recognition window, it's as if this termbase doesn't exist. I still can open it in Multiterm though, but that's it. I absolutely need to use this termbase, so I would very much like some quick help.
In the second picture, you should see at least 10 terms in the recognition window, but it's completely empty. I asked a friend to try it and she had the same error message.
I use Trados 2015 and my friend uses Trados 2019.

Thank you!