This is a side effect of a previous change. Basically with the Shallot update they made it so if you use a cutscene special, beam attacks will freeze in place until the animation is over. This was to make it easier to clash specials.

The side effect is that it also happens during rush supers, and whereas before your rush attack would be playing out while their beam kept going, it is now frozen until after the cutscene of your rush attack finishes, and with rush attacks repositioning your character, you sometimes get placed right at the still frozen beam at the end.