When Page Buffer Clear command is issued from the non-secure APB alias, ADDR must point on a non-secure region otherwise the command is silently discarded. For security reasons, the ADDR register is not accessible from the non-secure alias. The only way to change it is to write a data to the Page Buffer. If the intention is to issue a command that doesn't write the NVM (for instance an Erase Row command (ER)) then the PBC command must be issued to avoid locking further write accesses (even secure writes). ADDR must point to a non-secure NVM region when PBC is issued from the non-secure alias.