There is absolutely no reason to think those problems have anything to do
with systemd.
I have had a warning about my CPU fan from my BIOs. It's intermittent, I
have tons of cooling and the freezing does not occur when I would expect a
heavy load. (...) A lot of freezes occur while watching videos but also
compiling programs and just at random. My compute never freezes on it's own
while I am away from it, it's always while I am using it.
Decoding videos and compiling are CPU-intensive tasks!
More generally, random freezes under heavy loads suggest a hardware issue.
If the processor is not faulty, then it may be the RAM. Have you tested it?
You can install the "memtest86+" package, which is in Trisquel's repository,
and run it (from the bootloader's menu) during a night. If the screen turns
red, the RAM is faulty.
