This is a very strange log and it contains an error that is really rare: MCU 'mcu' shutdown: Watchdog timer!
This means that in the MCU something went wrong, leaving it in a “confused” state.
Given this error and your strange heating problem, I’d put my money on a dead or dying PSU.
Turn on both heaters and measure the output side of your power supply. If it reads significantly below 24V then you have your culprit.
Edit: Mind this when working on your PSU: Working with Line Voltage (110 V / 230 V / >50 V)