Ok so, where do I even begin?

The other day, I was building my computer-powered stove, and for some reason, when I tried to save my progress, the game refused to do so.

Afraid that I would lose the build, I tried to save the entire thing as a subassembly (important for what happens next), and tried to leave the game, but it didn't work.

So I force-quitted SP, and lost the original copy, but I rebuilt it again.

But that's not the problem here. Right after this, every time I left the game to go back to the designer menu, I get the below message:

I highly suspect that the faulty subassembly is the one I tried to save while my game hung. (Also, the game probably hung in the first place because it couldn't read an emoji label I made.)

I've been ignoring it for a couple days, but now it's getting on my nerves. So, is anyone able to fix this problem? I really appreciate your help.

Note: I'm on OSX (MacOS)