Guys. as said this is a test server - there is no traffic on it. This server definitely isn’t good enough for production use but that’s not the issue here. The question is why we do see postgres processes sticking like that (with 100% CPU usage) and slowing down things drastically. We were running the testserver with lower capacity even until a few days ago - it was only upsized due to the lack of disk size for a restore.
Production machine is running with 128GB of ram with the same Shared buffer settings without any issues - So I don’t think there’s a general issue with these settings and shared buffer size - especially not a private test machine without traffic.
But anyways - I will just redo the restore and see if something might have gone wrong as seemingly there’s not good explanation for the behaviour.