I had the same problem and applied the patch from @blogic from this thread which solved the problem for me.
There was some work done on hostapd on the 21.02 branch around November 23; looks like this patch has been forgotten. Maybe @blogic could take a look at it and add it back to the 21.02 branch?
Edit: This commit introduced append_radius_*_req_attr functions to 21.02 and caused this issue.