No, you're not the only one, had the same in 2 games now as well.
I don't have a screenshot or video, sadly.
Anyways, while moving Vel'Koz's tentacles are either pointing straight out stiff or they are rolled together, also stiff, they are not moving anymore.
Also the auto attack is a laser sometimes and the tentacle is not hitting the target.
Doesn't happen right at the fountain when the game starts, but starts to occur right in lane after about 2 minutes, sometimes Vel'Koz is shortly back to normal visual and auto attack animation but few seconds later he bugs out again, this happens as long as the game goes.
I had an Illaoi in game in both games, I don't know if that means something.