Same for me, got the Surface 7 Pro and slim pen together. The longest i've had is a run of eight days...then it crashed again. It seems to be on wakeup (for me). I've returned the surface and replaced it with a 7+ and it still happened. I've removed the slim pen and its been good so far (1 day 15hrs so far..)
I used the pen the other day without pairing (just using the tip on the screen) and within minutes it had frozen again. A restart fixes it , as does uninstalling the Intel driver, but the point is, I shouldn't have to do this at all.
I'd previously reinstalled windows, updated the driver package etc. Surely there must be a log of the freeze somewhere to nail this issue?!
I'll get a cheap older surface pen and see if it freezes again.