As far as I'm aware I don't have anything unusual running at 9pm.
Yes, it's entirely possible that the timing is random.
This is a fairly minimal build with just a handful of add-ons. I'd be happy to wipe it clean to a vanilla install with only the pvr.hts addon installed and re-test if that would help..... since I have a backup of all my key folders (.config / .kodi etc)
Just shutdown kodi, rename /storage/.kodi to /storage/.kodi.bak and restart LibreELEC then you will have a "clean" system with no additional addons enabled - this should be enough to test, and you can restore your original installation (if you wish) by deleting .kodi and then renaming .kodi.bak to .kodi.
PVR HTS has been implicated in OOM crashes but a definite cause is yet to be identified.
Seeing all the GPU memory returned strongly suggests Kodi is shutting down, or crashing. This is definitely abnormal behaviour so testing a "clean" system would be a start, and then introduce add-ons one at a time until the problem can be reproduced (the last add-on in theory being the cause of the problem).
Perhaps in addition to running bcmstat.sh, logging running processes might yield some additional information - run the following in a second ssh window:
then upload /storage/ps.log after the system has frozen and been restarted.