Look for any official documentation from the chip manufacturer regarding the SNVS module and its security features. This documentation might provide insights into the conditions that can trigger the security bits and how to reset them. If the code has worked for years and suddenly stopped, review any recent changes to the codebase or the environment where the code runs. Even minor updates or changes could have unforeseen impacts. Ensure that the power supply to the SNVS is stable and within the required specifications. Fluctuations or interruptions in power could cause the registers to behave unexpectedly.
