Ok, so pretty certain this is specific to my phone.
Browsed the recommended alternate front end for as long as I could stand it. Didn't get logged out, but I may have just not waited long enough.
Back on normal frontend, I deleted all browsing data (cookies, etc), logged back in and then got kicked out within a few minutes.
Rebooting the phone now. 🤞
Update: Nope, still getting booted within a few minutes. Beyond just using a different browser, I'm out of ideas, so I'll try that for a bit. 🤷
Update 2: Doesn't seem to be happening in Brave. So currently, only in FF, only on my phone, clearing cookies and rebooting did not help.
I'm open to any more ideas.