When using Focus you will lose the ability to move, be locked in place, at times.
The easiest way to reproduce this is to simply spam the ability 3-4 times quickly. I have mine bound to right click. However, this is a huge issue in normal gameplay where it locks you in place unable to move, without spamming it (perhaps unknowingly in the heat of battle tho). The only way to get out of it is to use flame rush. If it’s on cooldown, you usually just die.