Frequent errors that nobody can seem to diagnose...

About three months ago, I got a "check hybrid system" warning in my 2015 Prius Two. It was due for scheduled maintenance anyway so I took it to my usual shop that specializes in Hybrids. They said that after resetting the system the error code went away, and everything seemed to be working fine so I shouldn't worry about it unless the light comes on again.

A few weeks later I got the same error, this time paired with the ABS, brake, and skid lights on as well. This time I took it into a Toyota dealership who kept it overnight. They also came back and said that they were unable to find anything wrong with the car. They say that apparently there's some miscommunication with a sensor somewhere in the system, but since they can't replicate the problem in the shop they are unable to diagnose it. I drive it for another month or so without incident.

Flash forward to this month: I'm on the last leg of a 2,000 mile road trip when suddenly I get the hybrid, ABS, brake, and skid lights again. I find a Toyota dealership and they spend about 4 hours with the car only to tell me the exact same things I heard from the last two places. I manage to finish out the last few hundred miles of my trip to New York without incident.

Now I'm in New York visiting family and all the lights come back on again. I have now taken it to a third dealership, and after keeping the car for eight days they're telling me all the exact same stuff: there must be a sensor issue somewhere but the technician can't replicate the error so it's impossible to diagnose.

I've now paid diagnostic fees to four different technicians in three different states and they have all just kinda shrugged at me and said there's a problem somewhere but they don't know what it is. I'm at my wit's end here and not looking forward to taking this thing on the highway for another 2,000 mile trek back home.

Any advice?