Sonarr/Radarr connectivity to Plex: Failing

What Operating System?

Ubuntu 18.04 LTS

What is the problem?

When going to Sonarr/Radarr->Settings->Connect->Plex.
I follow the instructions here. When using the host ‘plex’, it always fails. When using an IP address it does work, but the IP addresses sometimes change when portainer is restarted, so this doesn’t work long term.

What did you already try to solve it?

Updated all containers to latest versions.
Restarted all containers.
Checked config against link above, and checked Plex network settings against wiki.
Checked portainer config: Originally Plex container had ?random string for hostname. Changed to plex. No difference.

Complete Logs

Logs help us with troubleshoting.

None provided…

Additional information

Portainer Screenshot…

are all containers on the plexguide network?

Well spotted.
For some reason plex had moved from the plexguide network to the ‘bridge’ network, as shown in the screenshot above.
I moved it to the plexguide network, and obviously it now works great.
Thanks very much!