Why when writing flash option bytes causes an infinite reboot cycle?

I'm running this code in my application and it continuously reboots. I've since moved the writing of the option bytes to the programming stage to avoid it but want to understand what I'm doing wrong.

 FLASH_OBProgramInitTypeDef ob; 
 
 HAL_FLASH_Unlock(); 
 __HAL_FLASH_CLEAR_FLAG(FLASH_FLAG_OPTVERR); 
 HAL_FLASH_OB_Unlock(); 
 HAL_FLASHEx_OBGetConfig(&ob); 
 
 if (ob.USERConfig & OB_IWDG_STOP_RUN) { 
 ob.USERConfig &= ~OB_IWDG_STOP_RUN; 
 HAL_FLASHEx_OBProgram(&ob); 
 HAL_FLASH_OB_Launch(); 
 } 
 
 HAL_FLASH_OB_Lock(); 
 HAL_FLASH_Lock();