I have found the issue for this, and hope that anyone else that experiences something similar finds this post and saves themselves a lot of headache
I tried to reupload over and over to no avail, eventually almost giving up and thinking the model was cursed, turns out it’s a wider problem with how steam family sharing works. I googled “generic steam error” because that’s the error I was getting before uploading successfully, and found this thread which ended by the person saying “oh oops I was logged into the wrong account”. I only have one account so that wouldn’t have been my problem, but I was sharing tower unite from my sister’s account via steam family sharing and was wondering if that was the issue. I’ve played this game for over 100 hours so even though we use a family account for all our games I figured I wouldn’t mind buying it again, and tried it after and it worked 100% perfectly first try. Moral of the story is if you get this error try seeing if you’re sharing the game from another library or if steam doesn’t flag you as owning it.