Remote Access Off Line--since new iMAc

Let’s maybe start with something simple… did you create an IP reservation in the DHCP settings of your router for the new iMac?
Such “on/off experiences” could be based on the router assigning your iMac a new local IP address when Plex is still searching the server on its old local network address.


Did you already have a look at the related troubleshooting support article?

https://support.plex.tv/articles/200931138-troubleshooting-remote-access/

There’s also a guide with some more details on how to troubleshoot remote access issues: