My lip sync animation is glitching but I can’t find what’s wrong with it.

This would happen before, but only ever in short bursts. This one is staying now for some reason. At first i thought it was just a visual bug, but it

It even appears after I exported it

I had to convert a snippet of the animation into a gif, which unfortunately caused it to be choppier than the original, but afew frames can be seen showing 2 mouth parts simultaneously. When I checked to see what happened in its symbol, it suddenly started playing normally. If anyone can help me I would be very greatful.