Once the watchdog timer starts counting, is there any way to stop it?
No. Once the watchdog timer starts counting, count can only be stopped by an MCU reset. However, when count source protection mode is disabled, count will be suspended during stop mode, wait mode, bus hold, and auto-program or auto-erase operation in EW1 mode. Also, if bit 0 of the FFFFFh address is 0, the watchdog timer will automatically start counting from the initial value even after a reset.