Can't change UNLOCK_1A after modifying in STM32CubeProgrammer on STM32U575

[ANiki.7]

Hello lovely people,

I seem to have run into a headscratcher that I can't get out of.

I have a NUCELO-U575ZI-Q that I've carried out the following steps on:

1. Connect board to PC
2. Connect with STM32CubeProgrammer Normal Mode, 24000KHz, SWD
3. Uncheck UNLOCK_1A in the Option Bytes Screen.
4. Disconnect and reconnect within STM32Cube
5. Attempt to Check UNLOCK_1A to reverse the protection
6. Encounter the following error:
   1. 
      

I've also tried using the CLI and can't get any different results, am I missing a step to be able to reprogram the option bytes?

Thanks in advance for your help!

[ANiki.7]

Possible solution:

If I raise the RDP level to DC. Then disconnect/reconnect. Then select AA on RDP, and CHECK UNLOCK_1A - the option bytes successfully program.

For some reason, both things have to happen at the same time (RDP regression, and the UNLOCK_1A byte being programmed)