For the last 20 hours or so, when I open the AC Forums app on my Pixel XL, it just shows me old threads and the spinning wheel of doom.
It happens from time to time. Close ACF from the recent apps and clear cache in settings - apps - AC Forums. It works for me every time and, unfortunately, it happens a lot
Glad it helped! Do you remember if the app stopped loading right after switching from WiFi to mobile, or vice versa? Most times I have the same problem is after switching networks.