How about a hard power switch? + crash report

[manawyrm]

This is by no means obvious.

True. 
I have encountered this same issue on my own PBP in the past and saw that there are enormous amounts of sysrq's happening when audio is played back at the highest volume levels. 
These have caused stuttering, lockups, hard reboots and other weird behaviour. 
That's not unexpected if you look at the list of available sysrqs: 
https://www.kernel.org/doc/html/latest/a...mmand-keys

For example "c" would produce this same output as shown Dendrocalamus64:
"Will perform a system crash by a NULL pointer dereference."