Hello,
Hmm, I see no issue in the code of FCCU itself.
Do you step debug the code or you run it over the FCCU config.
As FCCU config mode is guarded by config watchdog and you will get timeout if you try to debug configuration code. But such will not drop IVOR1.
If you see IVOR1, then check the details of the exception in MSCR register


I do not see this issue linked to FCCU, Rather some access restriction.
Identify the reason for IVOR1 then you will see where to look.
Best regards,
Peter