Bugged tuning won't let me upgrade my engine anymore

[TMT | Reol]

The Power Unit section in my Performance tuning bugged out on one of my cars and I can't install any kind of upgrades into it anymore. Someone said this happened after getting the Tuning from the Mechanic at the Parking Area, which I did do once. So that's what might've caused this.

I'm assuming this'll get fixed eventually but has anyone found a way to fix that right now, outside of selling and buying the car again?