Plex and Sonarr problems after newest (Buster?) update

A few days ago I updated to the latest DietPi (first with Buster?) and now I’m experiencing problems with both Plex and Sonarr. Qbittorrent, Pi-Hole, Aria2, and Samba seem to all be working fine.

Plex: I can play files already in the library, however the dashboard section of the homepage won’t load (“There was an unexpected error loading the dashboard”) and Plex is not finding newly added media when doing a library scan.

Sonarr: I get the loading screen with the Sonarr background and the dancing dots, but it never loads the UI. When I view the status with ‘htop’ after a reboot Sonarr is running, however after trying to open it in a browser it apparently crashes and is no longer present in ‘htop’.

After the update I saw some of the release notes pointing here:
I am a pretty novice user so that doesn’t all make sense to me, but I did run the APT key commands for Plex and Sonarr described there and then done apt-get clean; apt-get update.

Any tips?

hardware is Odroid HC2 (XU4)