Immobilize Bug?
I was about to post on this issue as well or at least a similar issue. I haven’t noticed if it occurs after being immobilized but there are times when I am unable to move unless I use some sort of “jump” type skill. Then I am able to move as normal again. I will have to check again to see if I was immobilized prior to the bug occurring.
Stun can also have this effect, so you get “stuck”. Its been there quite a while, but seems like the invisible bug its starting to grow on its own.