Posting here to confirm that instead of just 3-5 second freezes at a time, I am now experiencing FULL system crashes requiring me to force shut down my PC, with the 1.3 update...

After another 3 hours of playing this evening, unfortunately it seems disabling resize bar in Bios yesterday was a fluke. After about 2hr I started getting small hiccup freezes for 0.5-1s and then at around the 3hr played mark, the freezes were back to 3-5 seconds long, making the game unplayable. I did notice the textures upon spawn kept loading quickly though, which is 1 positive, but without a fix to the freezes / 100% CPU spikes, I'll have to take a break

Note; I tried the resolution that OP posted, and I turned off resize BAR in my bios, and after 3hr of play last night, I didn't have any freezes/stutters, and textures loaded in within 2-3 seconds after spawning (instead of taking 30-60 seconds as previously experienced). Too little testing/playing to say that was the golden bullet, will play again later today.

Interesting; I really don't want to downgrade / reinstall Windows just for 1 game having issues... I might just hold out in hopes that the next Windows version update fixes it, or Arma Reforger devs fix it.

Bumping this thread/report as I'm also experiencing the same issues/symptoms!

Throwing my hat in to the ticket/issue to hopefully get it prioritized higher!