Dissonant notes on certain strings - What could cause this?

[Davey]

I can't hear the issue when played acoustically - I don't know if that's because it's not there or if it's just too quiet to hear it unamplified. Originally I suspected an electrical issue but it seemed wise (and cheaper!) to check it wasn't just a setup issue first. Now I'm back to thinking it's electrical - either the pickups or something else. I don't know how I'd go about testing this though which is why I'd like a PRS tech to have a look at it. Although from the responses here it seems like the bridge still needs looking at too.

I haven't had a reply from PRS yet and it's been over a week so I need to get back on to them.

I've checked the cavities and there doesn't seem to be anything loose in them.

I would bring to the guitar to a qualified person to go over it and any good experienced tech will get the setup done "correctly" and once the setup is done, they can identify if there are any further issues and get those corrected as well.
Your current tech returned the guitar without solving the issue which means you need to find a better tech that can locate the problem.

 

[Jaymond]

The guitar is now on its way to PRS in Cambridge. They arranged for it to be picked up free of charge which is very good of them! Hopefully they can fix it. I’ll keep posting updates as I hear from them in case it helps anyone else in the future.