Hrm... the codpiece was changed, but I don't think it was changed in such a way that would break saves. It's still a piece of armor, it's just no longer upgradeable.
Viewing post in Save File Corruption and Overwritten/Modified in v0.3.10.4
I found the bug! It happens if you use a save created in a Patreon-exclusive version of the game in the free tier of the game; I just had it happen to me again; everything was immediately wiped back to Enchanter Level 1. I am assuming that this is to prevent people from cracking your game and punishing them, but if this is the case, it is also punishing legitimate users.
Edit: For clarity, I support temporarily on Patreon to get access to the new build, and then immediately unsubscribe (I get charged any time I want to download the new Patreon-exclusive build, but that's fine by me) because I don't want NSFW notifications in my personal email and I like being able to access my Patreon account without having to look over my shoulders/because I don't always want to see NSFW content. So I wanted to try out the new content without paying for Patreon exclusive but found out that my saves were nuked because I tried loading Patreon-exclusive saves on a non-Patreon version of the game.
As well, I can understand, assuming it was intentional, that you want to prevent people without Patreon versions of the game from cheating and getting Patreon-exclusive content, but it should just prevent you from loading the save, and not nuke it.
Oh, you're right, it is an earlier version... I see, I thought even though it had been nearly 2 weeks, that the free version of the game would be more up-to-date. Either way, I would have a strong preference for it to not nuke the save and instead just render it 'unusable' (I.E. an error message saying "This save is incompatible") In the previous case, I used the free version after using the Patreon exclusive version because I figured it was newer, and I ran into the same issue. Saving version information would be very helpful, and having the game recognize this version mismatch as well would be great.