We are facing a major issue for several weeks now with some 221E.
Many users can not connect to the FortiAPs as they get the message "Access point temporarily full".
In that exact time the access point may have 2 or 3 users only. Even with multiple reboots it may not be fixed
and I will have to proceed with firmware update in order to work properly.
Can anyone assist me with this issue?
This could depend on your FGT configuration as FGT also checks whether client is allowed to connect. As you mentioned, rebooting AP not solving the issue also points to this direction.
I suggest you open a ticket to Fortinet TAC who would be able to help you go through FOS configuration and collect right logs to root cause your issue.