Thermal runaway issue- stumped

Out of nowhere, I started to get a thermal runaway error on my Taz 5 running Firmware 1.9.34. I swapped out the SE tool head to another unit and still got the error. So I ordered a new V2C cable and a new tool head adapter, thinking there might be a wiring issue but after installing these new parts-- I still got an error 2.5 hours into a print. So, I then installed my M175 tool head and updated the firmware to 2.0 through Cura SE. I am STILL getting an error intermittently on every 2-3 prints over 3 hours. I’m completely stumped. Is this now a board issue? Is something failing there? I did watch the nozzle and bed temps occasionally and found the nozzle meandering between 195 - 208c on a print set for 205c. The bed was stable at 65c. I have never been at the printer when the error happens.