One of my customers has reported this error that he's getting, and he gets it on both his own site that I'm hosting for him, and on my site. The only common thing is the XF version (2.2.13), and Cloudflare.
After inactivity ( usually overnight) if I click the notification bell if there are alerts I get the error. If I go into the forum first then I don’t get the error.
The only other thing is it seems to be on Apple devices, as another member of his site on Android hasn't reported ever having it.
Would a change of IP or invalidating a session token somehow cause this?