Okay so I searched on the devforum and google and I couldn’t find anything about this except for this one post:
Unfortunately OP of that post didn’t find a solution for the problem. However, I noticed a similarity between this post and the post I linked to and that is you both use viewport frame and both errors are coming from a “Animate” script so maybe, just maybe the error is related to something caused by viewport frame or the roblox animate script.
I know, there isn’t much to go with but there is no other lead to go with now and I couldn’t reproduce the error myself to help you with it. Sorry.