RL_Dane, (edited ) What in the world is wrong with this machine?
Something as simple as syncthing running, an apt upgrade, or even just doing a dd of a gigabyte from /dev/zero to a junk file can cause the system load to scream up to 10 (quad-core system), and it starts freezing.
Do I have a dodgy SSD???
Update 1: I am using full disk encryption (LUKS)
Update 2: gsmartcontrol output https://bin.benjaminhollon.com/fersimebia
Update 3: I'm going to try copying everything over to a spare SSD later.