2013 Prius Suddenly Slows to 15mph; Restarting Fixes It

Hello! Sorry for the novel, but I don't want to miss any important detail. I've been dealing with an issue for almost a year now on my 2013 Prius (~90,000 miles.) I'll be driving and suddenly the slip light (traction control light?) starts flashing and the car slows to max 15mph. It first happened while I was going 30mph and I thought I blew a tire. It has since happened too many times to count. I can be driving on the highway and it'll rapidly slow down and I have to pull off onto the shoulder. It has also happened at roundabouts, city speeds, and even stopped at a stoplight (the slip light goes on and I have to crawl through the intersection). It makes a squealing, grinding noise, like I'm driving with the parking brake one.
But, if I turn the car off and on again, it'll drive normally for the rest of my trip. If I try to drive through the resistance, the car won't go past 15mph. The slip light stops flashing when I brake, but starts up again as soon as I accelerate.
The problem is no mechanic can seem to recreate and diagnose it. I took it to my regular mechanic first and they were able to recreate the issue, but they referred me to the Toyota dealership since they didn't have much experience with Priuses. The Toyota dealership couldn't recreate the issue, didn't see any codes, basically told me to drive it until it happens more often. I took it back to the used car dealership I bought it from. They said they got a code for a faulty wheel speed sensor, which they replaced. Weird that they got that code, but not the Toyota dealership, but whatever, I hoped that would fix it. Nope. It started having the same issue within the week. I took it back to the Toyota dealership. They checked all the wheel speed sensors, said they saw no issues. Still no codes. Still couldn't recreate the issue despite driving on the highway, through bumpy streets. At one visit they told me they got a steering wheel angle sensor code, but they said they reset that and it wouldn't be the reason for the problem.
I've taken notes of when it happens. It seems to be worse in the summer, but that could just be because I'm driving more. Rain and snow don't seem to make it happen more or less. If I sit in the car idling for 10 minutes and then drive, I think it's more likely to happen. If I drive for a couple hours, it's almost certain to happen. It also tends to happen when I'm turning slightly (on highway offramps, roundabouts, or switching lanes on the highway).
I'm at a loss. I've been to three mechanics 9 times now over the course of the year. I don't drive on the highway after a near miss when I suddenly stopped last December. Most frustratingly, it happened on the way home from the mechanic, 5 blocks away, and by the time I limped back the car back to the shop they were closed for the night. Any ideas for what might be wrong would be greatly appreciated. I'm almost to the point of selling it for parts and buying a bus pass.