Interesting that the problem cropped up after you tweaked the set-up. FWIW, I have found that treble-side strings, like a G string, will lose power or what I would prefer to call a full frequency response if the action of the bass is just a tad too low on the treble side. In fact, that happened to me last week.
If your action is a bit too low, the string won't audibly buzz (like the B, E or A strings will), but its ability to vibrate freely will be affected if it's bouncing off the fret tops after you strike it. (Of course, if the action is waaay too low the D and G strings will buzz, too.)
Anyway, try raising the treble side action no more than a 1/4 or 1/2 of a bridge wrench turn and see if that clears up the problem. Bet it does