Monsters throughout campaign becoming randomly (periodically) invulnerable

Playing SSF R right now,

I'm only at Act 3 so far , but I've noticed this as early as the first zone of Act 1. This is happening with ALL types of mobs, and it's happening so often it's nearly every pack of enemies. Monsters are randomly becoming invulnerable for a few seconds, then able to be damaged again for seemingly no reason.

This is not any enemy totem, or magic / rare modifiers, this is also not isolated to any particular areas, it's happening everywhere, and even with normal monsters.

I'm using Molten Strike right now and I had phantasm support linked to it initially, and was noticing the mobs not even take damage from the phantasms too, so it's not just player damage.

I can stand there and swing indefinitely on the mob, it will attack back and do damage to me, but until I either I move or it moves, it won't take any damage, feels like some kind of weird networking de-sync.

When this triggers is also seemingly random, it can happen at the beginning of me attacking the mob (I immediately do no damage, mini-life bar doesn't even appear), or it can happen randomly during the fight (I do some damage, then it just becomes invulnerable, if the monster has ES , the ES will just start recharging as if I stopped attacking, meanwhile I'm still swinging and molten strike is triggering)

I'm not missing, I have 100% chance to hit / 100% chance to hit evasive monsters.

Here's a video of one instance of this occurring for context:
https://www.youtube.com/watch?v=2yp1NdxemMI