It’s lag. Also if to many CC’s happen at once it’s almost like the server can’t figure it out and just says “well, good luck!” I don’t think anything fishy is going on. Just lag.
As annoying as it is. Most of the problems are around the CC, not the skill itself. There are a few skills that have put me in an unbreakable CC lately. Though incap is probably the most common.
When that CC does knock you down and becomes unbreakable the animation is of you sitting back up but sliding sideways at the same time. It's the same as Templar Javelin and usually happens after jumpi