Are you using the BFQ I/O scheduler?
If yes, then please read this:
https://lore.kernel.org/linux-block/[email protected]/T/#t
Synthesis: There was a faulty commit regarding BFQ, known to lead to hard freezes.
Workaround: use another scheduler, like “none” or “mq-deadline”.
Correct, but bisecting is usually time-consuming 
I actually spend several hours to find out…
I’m quite sure though that this issue is due to commit 88013a0c5d99 as mentioned in the above kernel thread.
So please try switching to a different I/O scheduler for the moment being and see if it helps.