K1 Max bed temperature sensor

Two months old, no problems at all until today. Started a PLA print at 220 degC nozzle, 52 degC bed. Print stopped at beginning of first layer, saying the bed temperature was behaving unexpectedly. The (bed) temperature was reported at 84 degC, but was cool to the touch. Switched off and left to cool everything down to room temp. Restarted with a different print, has started working normally, but the bed temperature target 52 degC is creeping up, reaching 70 (reported) after about 15 mins. I have no means of verifying the actual temperature, but a finger test feels cool, like about 30 deg.
Anyone else had issues like this??