I've seen several posts involving odd electrical behavior, but not this particular combination of symptoms.

My 2012 Elantra frequently but intermittently goes dead, clearly because the anti-theft system has been triggered. I have checked both the battery charge and the key fob battery, and both are fine.
About half the time the car unlocks and locks with the key fob without any issue, and the car starts up with a strong ignition turnover, so the battery seems fine. The other half, several different scenarios unfold:

The car will not respond at all to the remote unlock button at all, and I have to manually unlock the door with the physical key. Sometimes that brings the car back to life, sometimes not. Sometimes the alarm sounds, and I can turn it off immediately with the key fob and be on my way. Other times, the car remains shut down electrically, I put the key in the ignition, and it turns over. Other times, I put the key in the ignition and I have to wait about a minute for the system to reset, and then it comes back to life.

On some occasions, all is well until I turn they key, the electrical system blinks off (clock re-sets to 1:00, radio station pre-sets are erased), and then it will start up.

The shutdown occurs most often after the car has been sitting locked in the driveway overnight, but it has also happened just after pumping gas, and it's dead when trying to start up again.

So far I have always been able to get the car going again, and when it works, all is fine for several start and stop cycles for a day or two, and then it shuts down again.

Taking it to my usual mechanic (not the dealer, which is about an hour away), he was unable to replicate the problem (of course!), but also was unable to access/read any of the sensors related to the electrical system.

Any idea what could be causing such a collection of symptoms???