In the second video, That engine IMO appears to have at least 1 dead cylinder. that could be due to any number of things. I would start by isolating cylinders and proceed with the diagnosis once the cylinder is identified
You also mentioned valve train noise, could be a clue there

I also did not see any coolant moving in the upper hose, Maybe the RPM was too low ?

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I have confirmed combustion in the coolant from a sniffer test as well.

Time for a tear down IMO