Weird system freezes.

It's the third time my system randomly froze and did not recover.
The first time it has happened I was playing The Finals, the system froze mid match, out of nowhere. The second time it happened I was only launching that game, the system started lagging like crazy during shader precomp, and froze after like 10 seconds. And the third time happened ~15 minutes ago, when I was doing wplace stuff, nothing intensive.
How can I diagnose this issue?
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