Anything over 80 degrees and direct sunlight I'll get the same readout on my SMO25. I use a beach umbrella to keep it cool but if it's windy I've also used a damp dish towel and gently wrapped it around the temp readout box which houses the electronics.
Of note, every time it resets it will fire up the heating element like you are just turning it on. I believe it goes on full blast for 10 minutes before it will idle. Let's just say when this happened the first time and I was smoking salmon it didn't turn out so great when temp hit 275 degrees on me