Fresh moves works perfectly for other skins I have, but one I made recently has been extremely buggy. The pupils flicker in and out of the iris, and I've noticed they completely disappear if you're looking even slightly down, but if you're looking straight up they seem to work just fine. This looking down issue extends to the idle animation of the pack, the pupils flicker and/or disappear when the player model dips down in the idle. I've tried everything, including the black eyes fix (even though the iris is black already) and nothing works, and it's only this specific skin. Could someone please help?

From what I can tell this is actually a bug with the Modrinth app modifying your skin. It has been reported to Modrinth. Uploading your skin through the Minecraft website or Vanilla launcher fixes the issue.