Check if the Plex Media Server is still in the same Local Network. i had the same Issue after Updating.
check this and try it out. maybe it fixes the issue for you too.
I updated my TrueNas and had to setup the Docker COntainer again because between TrueNas Versions they changed how the “Apps” works. but in the new Docker Version were more settings to do. so i had Explicit click the Local Host checkbox so the Plex Media server got the correct IP Adress. otherwise internal it get the IP Adress that the Docker Container Priovided.
