Sometimes without any reproduceable reason my project with STM32F767 does not power up. If this occurs Read Out Protection is set (which I definitely do not have done) and Option Bytes are scrambled: BOOT_ADD0 and BOOT_ADD1 are set to 0xffff. In this case STM32 seems to be "dead" (does nothing). But I can access it via STLink and reanimate it with a "complete erase" following reflashing firmware and new setting of the Option Bytes. This is not reliable behaviour for releasing the project so I wonder what can be the cause for this. Vcc is 3.3V stable, coming from a LDO from 5V supply. Capacitors near to MCU Vcc pins are present. Maybe it is important that I am using RTC circuit with connected CR2032 as RTC battery. Any help is welcome - I do not have any idea where to begin investigations.