2017 Yukon Denali 60k miles
Has been a no issue vehicle but last night I noticed it seemed to be cycling the high beam lights on/off but all other systems seem ok. When I arrived home hit the engine stop button and all systems went totally dead, like you pulled the battery out. No dash, no lights no door locks, dead mackerel dead.
Could not revive it so left until morning.
today all seems fine. Under hood all looks fine, battery checks good and connections are tight.

Any guesses?

 

Welcome from Florida. From your description it seems like you have battery or battery cable problem. Check for corrosion and looseness at both ends of both cables. How old is your battery?