In the manual page 250 I read
The free watchdog timer can automatically start at power on when the hardware free watchdog timer bit in the device option bits is set.
And from the datasheet
0x1FFF F800 - 0x1FFF F80F: Option bytes
and again from the manual
So bit 0 of the option byte stored at 0x1ffff802 determines if the free watchdog timer is started from hardware on powerup or via software. Can you readout that byte with a C pointer (I believe for reading from this address you don’t need any special unlocking voodoo) and print it via UART?
Do you know if the option bytes were ever modified in this chip? If you have multiple chips, do they all behave the same?