Small anecdote, but I was getting print failures a few layers in with thermal runaway as the error code (with tiny oscillations of temperature fluctuating at the target temp seen on octoprint) after replacing the hotend for all metal (bimetal heat break, CR-10 copper block, screw in NTC 3950 thermistor) on an Elegoo Neptune 3 Pro. Turns out that the little silicon cover for the block was missing, and replacing it completely solved the issue.