I always had this problem but it used to be rare (only when playing several matches in a row, about 1/50 match). My computer would just restart during a match and take up to 10 min to restart (vs. about 2-3 min normally).
But in the last few weeks it became unbearable, it makes my PC crash 1/10 match and I can't even rejoin because it makes my computer so slow to restart.
I tried many different things - fresh reinstalls, launching the game through the openGL exe, I tried to look into log files. I thought it could be overheating or a memory leak, but I wasn't able to find anything.
It's the only program causing this issue on my computer - I don't have trouble with more demanding games like XCOM2 or Monster Hunter World, diminishing graphic settings doesn't change anything. It looks like a hardware issue but I can't find the problem.
What can I do? I'm starting to be a bit desperate here...