You have answered your own question, really: it's likely to be overheating. Change its location to somewhere that is cooler and/or better ventilated, keep it dust-free and use little rubber feet if it doesn't already have them.
Surface Pro (2017) vs Surface Pro 4
20 groundbreaking 3D animation technologies coming to Siggraph 2017
iPad Pro 12.9 vs Surface Pro 5
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.