Rear glass replacement is always a tricky issue for repair. The main problem is the adhesive used to hold the glass on is extremely strong and requires high heat to soften enough for removal. The more expensive repair facilities use a precision laser to burn away the adhesive with minimal damage to other components, but most simply use a heat gun to blast the back of the phone with heat in order to get the old glass off.
This sometimes has the unfortunate side effect of damaging internal components of the phone; we've seen cameras, flex cables and other parts that no longer work after a rear glass repair. The only truly safe way to do that repair is to remove all of the internal components first; basically you have to gut the phone, which can have its own set of problems, but at least you don't run the risk of heat damage.
So anyway, it might be worth your time to try software solutions first such as doing a complete wipe and restore, but my personal suspicion is that you'll end up replacing the rear camera to fix this problem.