This may not be a Minecraft problem, but it has only happened whilst playing. The computer freezes completely – the clock and cursor stops as well. Can only do a hardware shutdown with the physical on/off button.
So no log is created either.
Mostly throwing this out there to see if I'm alone with the issue or anyone else has experienced the same problem.
(Never experienced the problem in 1.8.)
Not a Minecraft issue. Graphics card and CPU may be overheating (pull the dust bunnies out of the cooling fans), etc.
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