Hi there! I can confirm that this is accurate. The itch.io version is based off a very old build which uses the original (outdated) backend. Due to major changes and optimisations, the Patreon version has significantly better performance. Ie. Users have reported that operations that used to take more than an hour, are now finishing within 30 minutes or less.
Well, the hint in the mail gives you everything you need. And once you figure it out, you will kick yourself because it was so obvious. I'm not comfortable giving any more hints, because the dev clearly doesn't want the password being mentioned here. If you absolutely can't figure it out, he mentioned the Discord as the place to ask.