It usually happens when you move the cursor around while channelling. It gets stuck on random indestructible objects and decorations and won't move until you stop channelling, move the cursor away and start firing again.

The culprits can be visible, like various anti-tank obstacles in the winter map for example, to barely visible, like the one in the screenshot, to completely hidden that you only find once they grab your channelling beam (and which the devs probably left in by mistake).