Upon trying to add a new skin to my library, an error message comes up saying "Unable to add skin to library", and whenever I try to save my current skin (which I added via minecraft.net), it says "Unable to duplicate skin" with no workaround I have found.

Potentially related: On occasion, running the exact same settings and version, my game will crash upon opening with exit code 0. I'm not sure if this is related, though.