Well, its night here now. Temp is 90 °C / 194 °F. I said this was a 900mhz SM, but its instead a 5.7ghz P9 SM. No, its on a tripod on a roof. No cover, have never needed to do so so far...Yes, it is open to sunlight. I have never had this problem before.
Temperature, power level and other things on the P9 board will be highly inaccurate if the calibration data is wrong. Registration/session problems can be one of the symptoms.
I would go swap it out. Then open a Cambium support request and ask for the calibration data for that SM's ESN. Boot it up with a default plug inserted. That should give you the Configuration > Radio Calibration page.