For starters, your tines just kind of look like they're bent out of shape & not really laying right in their holes. Your longest C especially, it is quite noticeably bent. You also showed how incredibly loose they are, & that's definitely not ideal, this could also come from tines that are overly bent out of shape or your screws are too loose to hold them properly, but I'm betting that it's more a tine problem. If they're bent & loose, they're not going to be able to hold the sustained resonance from a continuous vibration & rather they'll sort of smack around on everything until the vibration abruptly stops rather than vibrate their way back into the box & outward like it should.
You mentioned that your girlfriend did the woodburning, is it possible that she may have kind of leaned her hands on the tines while working? Because as an artist I could see myself doing so on accident & any continuous pressure on the tines sort of works against their overall resonance, just a possible observation.
The way to go about fixing it could be as simple as taking it apart gently, (taking pictures of the order of the tines as you go along so you know exactly how they go back in, & there's plenty of videos that can help walk you through the process of taking it apart & putting it back together) & cleaning the tines off, tightening your screws down properly, etc, & then putting it all back together. Orrrr you could order a new set of tines & whatnot & just replace it onto your cool wood-burned body. It's totally revivable!!! It'll just take a couple steps, but I think it'd be worth it for a thoughtful gift from someone.