Brand New machine.
Ender - 3V2
Main board overheating causes long runs to fail.
Known issue with new machines.
The print starts level shifting on long runs.
Then a clunk starts as the processor overheats.
After a long run the machine freezes up.

I'm trying to get a refund. I'll update when successful.

I have the same issue. My E3 V2 is from December (this week). I've checked all the screws and bolts, all the belts look good. No binding on the Z axis. It works good for an hour or two at the most now. I hear the clunk and see the level shifting. Any long program fails. I have also another clue that no one has mentioned. NOW it freezes up after a couple of hours. I have to power it down, and restart. Thats obviously a processor error from the main board. I'm asking the factory for a replacement. Perhaps we should be replacing it with a different model. Perhaps a new model has a different circuit board that's not bothered by heat.