This was a replacement for a Surface Pro 3 which has served me faithfully for years, so I'm already an entrenched fan.
In my case it looks like an old USB-C Microsoft Display Dock I was testing was causing the problem. Stopped using it and the issue hasn't returned.
Given USB-C is new for Surface Pro, my guess is that's where the issue lies, with some device drivers being overwritten with incompatible ones.