I had something similar happen... my side markers did not light up. It was the night before a trip. The next morning before pulling out they miraculously worked. Recently, an LED interior ceiling light did not turn on, but a moment later it worked as normal.
This odd phenomena, it has been suggested, could be due to LED fixtures easily becoming "masked" by dust that the extremely low voltage then needs a little more time to burn off. In my case, it turned out there was nothing wrong.
"A billion here, a billion there...add it all up and before you know it you're talking real money." Everett Dirkson