My experience is almost exactly like
@Dan Albrich. I exit the car normally without any thought or concern about the auto locking. In two years, I can count on one hand (and have a couple of fingers left over) the number of times it hasn’t worked and has given me the rapid beeps to tell me it didn’t lock. FWIW, my fob is in a leather Lexus cover in my front pants pockets or if jeans, it’s in the little pocket watch pocket. And when in the main pocket, it’s behind a large metal hunk of the Second Amendment and still works almost perfectly.
This is one more area where we have reports of our Claritys seeming to act quite differently. Long distance trouble shooting is difficult at best but logically it’s either the car (sensors, antennas?), the fob (damaged, malfunctioning, low battery, ?), or the operator (phone or other metal blocking the signal, ?). Or if it only happens in specific locations, it could be interference. It’s usually a tough sell to the dealer’s service dept. when you have an intermittent problem that’s not throwing any diagnostic codes and wont reoccur when at the dealer. If you can get the service advisor to put your fob in their pocket and get in and out and get the rapid beeps, you might be able to get some warranty work done to track it down. I hope you can get some resolution on this as I imagine it is very frustrating.
You might try:
1. Swap fobs for a long enough time to see if it only happens with one fob. That would suggest its fob related.
2. Try it with the fob being the only thing in that pocket and with nothing in a jacket pocket over it.
3. Try a fresh battery even if the low battery warning is not present.
4. Try recording as much information about when it happens, like location, temperature, speed and angle you walked away, etc. to see if there is any common denominator to the problem.
5. And as much as I hated it when the IT guys at work wanted to reimage my computer instead of trouble shooting the problem, you might try a hard reset of the system by disconnecting the 12V battery. It will sometimes “magically” fix the odd electronic “hiccup”.