Had the oddest thing happen to me last Sunday night.
Went to go grab something out of my truck (2014 F-150 XLT, 66,000 miles on it) and the keypad wouldn't light up to get in. Went to grab the key fob, tried to unlock it, nothing. Manually unlocked it, no electrical at all, key in ignition and turned, the car is completely dead. Wait until morning to call the insurance company to get it jumped. Jumped, starts up, go straight to my mechanic. It has a new battery and is still new enough that the alternator is still healthy.
Get a call a few hours later. Everything checks out. Battery is testing as new, alternator is charging the battery and in good condition, fuses all intact, solenoids, ignition switch, all good. Ran it through the computer, no problems or errors detected. Cables in good shape, tight, nothing to be found and starts up like a dream.
They had five people look at it and no one can find an issue. I've read a few other posts from people that say it's happened to them and just magically works, some say they just have to hit the unlock button inside and it works again. It's just so weird and it was kinda nerve wracking all week starting it up. It was also weird that my remote start was always sending me back a signal that the car started, even though it was dead and didn't start.