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I think your problem is, as you might guess, somewhere in those connectors. I had a related problem with thermal runaways on my Mega Pro. It seemed linked to motion- and someone suggested the repeated connectors between the thermistor and the motherboard were the problem.

I took off that daughterboard, bent the T0 pins a little to point off the the side a bit for access, and made a cable with dupont connectors, which runs out the hole for the bed wiring, and connects directly with the thermistor on the other end. (Forgot to mention I replaced the daughterboard for its other functionality. There's a little connector between it and the T0 connector, which should be discarded.)

Wiring the thermistor directly (save for the dupont connectors) to the motherboard solved my thermal runaway issue. (This was something Anycubic tech support could not do.) No guarantee it will solve your problem- but it is definitely worth a try. You can test this by attaching the dupont connectors before bending the pins- and obviously without actually having to install the thermistor you use for this. In a maker space, finding someone who can easily do this simple wiring should be MUCH easier than it was for me to teach myself how to do it. :)