So, I love this game. I managed to get a character to over a thousand tons... at which point, she somehow gets a negative weight, meaning I'm forced back into the initial apartment and unable to gain weight, so that's a bit of a save-bricking bug... I tried exiting and relaunching, and the same thing happened before terribly long. Help?
Unfortunately that sounds like an integer overflow error. I think that character's pretty much broken for a long time until you can get them back to positives again.
You can stick with it until you manage to get past the negative plateau but I'd just delete that character and make a new one. It sucks but there's not much else to do at this point.