Hi there.
I’m not completely sure but your description of the bug sounds like the one I encountered a few weeks ago and I asked for help here: V9.1.1 - bug in event list block when using specific topic filtering? - #7 by RobR
In the meanwhile the bug I reported has been fixed with the upcoming version 9.1.2. See the issue in github: https://github.com/concretecms/concretecms/issues/10808
Hope that helps.
Cheers, Rob