Matthew, I noticed mine gets hot too, but not so hot i can’t touch it and keep my hand on it. however the problem happens all the time, even on days/nights where the outside temp is in the 60s & 70s, i’m very confident during these times it isn’t over the 149F max.
mine is mounted in a (vented) plastic waterproof case - so pretty much the same thing as mounted to a wall. maybe it’s not getting enough ventilation out the back? dunno… i’ll try putting a spacer in between the wall and the modem to increase airflow. while i don’t think the temp is the problem, i don’t know - so ill look into throwing a thermometer in there with it - but it isn’t easy to access, which makes checking it a real pita
i do use PoE to power the peplink, but i do not use the Peplink to power other devices (i don’t think it has enough power to do so, but i haven’t really tested it).
please let me know if you learn anything by updating this post, i’ll do the same. i’m really hoping we can solve this, it’s brutal. good luck!