Finally, FINALLY found the solution to this vexing problem!!!
Took the car to the dealer twice about this problem. To no avail, since they could not reproduce the problem.
Both times it was hot summer days, and the problem did not manifest itself at all. Dealer was totally unwilling to do anything, even with my multiple videos showing the problem many mornings. It was an exercise in wasted time and futility. This is when I knew I had to deal with the problem myself, even if the fix had to come out of my own pocket instead of Honda warranty.
As with all of us with this strange problem, the problem manifests itself mostly after sitting for hours during cold nights or days. It affects both sliding doors equally......in that no handle, button, or remote will automatically open either door.
I utilized this forums' links to find wiring diagrams for the entire sliding door and keyless entry system. I analyzed the wiring diagrams for quite a while trying to figure out where the fault might be. It could not be with the individual door controllers, electric hinge, or wiring, as they are pretty much independent according to the wiring diagrams. The only control commonality between the two doors was the master Power Door On/Off switch on the left side of the driver's dash. I also remembered that the sliding doors usually started working after messing with this switch.
Looked up the Honda part number and found that this switch was relatively cheap (< $25 most places online), so I wasn't really risking much by buying it outright.
Bought it, replaced it, and sliding doors have worked 100% reliably ever since!!!!
Here is the Honda part number for your 2011+ Odyssey if you suspect you have this specific problem:
This switch is a combo assembly of driver's left and right sliding door control, and master switch for sliding door on/off.
You don't even need any tools to replace it, just a flexible arm to reach under the dash and push the switch assembly out. Once you push it out, you can detach the wiring harness by pushing down the locking tab and removing the harness connector. Super simple.
After busting the old switch open, I can see exactly what the failure was. The master on/off switch is simply a metal contact that slides back and forth on a Printed Circuit Board. This contact pulls down to ground both door controller's master enable, thereby enabling or disabling both sliding doors. The reason this problem manifests itself at night or in the cold is that the metal traces on the PCB get worn, and as the PCB, metal contact, and plastic shrinks ever so slightly in the cold after sitting for a while, it loses ability to hold a strong connection thereby disabling both sliding doors.
Ever notice how this problem NEVER manifests itself when your Odyssey is nice and warm inside? This is why.
IMHO, this appears to be an economical switch design by Honda that will not stand up to extended use. My advice is to switch it to ON or OFF and leave it that way. Doesn't look like it will stand up well to constant switching.
Anyways, this is what worked for me. I don't make any claims that it will help your specific problem, so please don't message me if this doesn't work for you. However, I truly hope it helps somebody avoid the frustration that this problem has caused my wife and I with the sliding doors on our 2014 Odyssey.
Good luck to all!!