Ran into same issue this morning, added a new router behind AT&T BMG320 and enabled passthrough. New router changed subnets.
I had to update network settings in two different places, under Network / Global Configuration and Apps / Settings / Advanced Settings. On Advanced Settings I also checked Force. Additionally, not sure if this helped anything, but on Apps, selected Choose Pool and selected the "apps" pool I was already using. Rebooted and everything started coming back up slowly.
I'm now in the aftermath of changing all of my references, thankfully all my apps are back up and running.