not the only one with this
if your still in control of the cart try and move to a more open area (use the horse as a guide as to where the cart should be
generally the only real fix is to start again, due to all the other issues this little one cause's, such as 'ice skating' and 'world rotation'
<edit> never mind they brought out a character and horse/cart reset tool https://itch.io/t/129731/character-sheet-fix should be second post