I was just able to watch your video. Welcome to the club.
I’ve been having this problem since around August/September. I’ve had friends with the bug back before the challanges book update and the summer soltice patch. It seems to get randomly fixed during future patches and then reappear in new ones. The only fix is to switch to DX11, but even then, in most cases you will drop to 20-30FPS during hordes.
The Dev in charge of the engine wasn’t able to figure out what was causing it. If you pull up your GFX stats while this bug is happening, you’ll probably notice that your GPU is locking up, going to 0% usage during the freezes. Another fun thing, if you’re hosting, when the freezes happen, all your clients will see the mobs freeze during your freeze.
There seems to be no fix. You can find threads on this bug going all the way back to April. It’s unknown what causes it to trigger, and why it only affects a small amount of the population.