Q: passcode

Hi

If you have already tried suggestions including checking that Wrist Detection is turned on, wearing your watch sufficiently snugly, restarting your watch and unpairing & repairing your watch, then I suggest that you contact Apple Support (mail-in service may be available) or make a Genius Bar reservation with a view to having your watch checked under warranty:

https://www.apple.com/support/watch/contact/