Good news! I found the issue and was able to work around it. I think there may be an engine bug related to CanvasGroup. I have two types of objects that use a CanvasGroup outline shader: the serpent and the cannon barrels. For some reason, whenever a cannon is on screen, it causes buggy rendering with the serpent. I stopped using that shader for the cannons and now the serpent renders fine on Chrome/Mac OS.
Pretty odd issue, but thanks for your help tracking it down.
Make sure to check out the jam page after the voting is complete that fix and a few more we found after the deadline!