Yeah, I assume it's overheating causing this. There is a different manifestation of the problem between the two recorder versions in my case, but the over-hot situation is the same.
Mk1 would produce a sort of rhythmic brief mute and level-pumping, which moved across all channels in a sort of wave like way, perhaps due to the phantom power cycling after the deck became overheated. With the mk2 all analog input levels suddenly dropped fully zero and remained muted. Due to the digital input still working, I assume that this was also a phantom power issue. I was not recording to any of the analog inputs without phantom, so not sure if those would have remained recording or not.
I propped open the Tascam form-fitting case to allow some additional cooling air ventilation this last weekend, and had a single-use instant cold-pack on hand in the bag just in case, but the mk2 didn't get very warm at all this time without the V3 also running in there right next to it.