Whenever a character moves over a part or jumps and lands on a part, the very bottom of their feet clip into that part slightly and then a couple fractions of a second later they pop back out. Example:
This can be observed by creating a new place in Studio with Ctrl+N (happens with or without plugins), going into Play Solo, and jumping up and down on the baseplate (or any other part you create). You can also observe it in Play mode in this empty baseplate published to the site: https://www.roblox.com/games/256000089/EchoReapers-Place-Number-169
I’m fairly certain this is a recent problem because I had never noticed it until today.