To late. I set the value to 50GB. But since my cache pool still shows 300GB of free space, this shouldn't be a problem, even if it might not solve the actual problem.
By the way, thank you for the instructions! In principle it worked and fixed the problem! The containers are running again.
However, I now have a new problem because a container is not working (like before). I guess I should post this somewhere else?
The Sync-Thing instance is not reachable; in the log I get a warning message:
"2024-03-20 17:56:08,284 DEBG 'start-script' stdout output:
[start] 2024/03/20 17:56:08 WARNING: Error opening database: read /config/syncthing/data/index-v0.14.0.db/000037.log: input/output error (is another instance of Syncthing running ?)"