If you login to the User Search and use the Advanced Search to view Inactive Users are the users indeed Inactive? Perhaps they just need to be activated.
This can happen if you put an approval step in place for the registration.
Thanks for coming back to me. They are active, and I’ve double-checked.
However, they have been able to edit previously, so it’s just weird that it’s happening to them now. They have tried in both Edge & Chrome and get the same issue whereas if I log in as them/me I don’t get the issue.
One other thing I’m wondeering is if their IP is changing or something during the same session- You might try turning off IP fixation in the dashboard and seeing if that helps. Under here, untick “log out if user IP changes” and see if that helps:
/index.php/dashboard/system/registration/automated_logout