Upgraded the box containing #mastodon installation of https://social.diva.exchange from #ubuntu 18.04 to ubuntu 20.04. That was a rather painful process and this mastodon instance experienced some downtime 😭. Sorry for that. #mastoadmin
#ruby was the problem (some versions of shared libraries were not available anymore on ubuntu 20.04). This issue helped us solving it: https://github.com/tootsuite/mastodon/issues/14987.
Long story short: "bundle install --force" within the mastodon/live folder solved the ruby issues. 😀