Had that problem as well. Got tired of trying all the usual fixes, so loaded the game and played without the trainer enabled until I got into the area. The trainer worked perfectly after that. Just try and keep from getting killed for a short time.
That happens if you take the chest's contents before it's done opening. It just bugs out because the trigger for closing the chest doesn't get processed when it's still opening. Just wait half a second longer for it to finish playing the open animation.
If it happens anyway, save & quit and load back in, that'll fix it.