That you can ride 30 or 40 minutes is extremely encouraging. If you do that regularly and it is a positive experience keep going. Minor upper back and shoulder stress is normal for cycling. If regular cycling is making things worse just stop until you get advice you can trust. Good advice is advice that makes riding easier. You are the judge.
I take a dim view of fitters. First query to fitter would be how much does he know about ACDF surgery. If you are still seeing a PT ask them what they know. Or if you simply had a good relationship with your post-surgery PT, get back to them, have them review whatever you get from the fitter.
The guy around here who has a really good rep for fits, I've known him since he was five years old. Knew his father. He expresses frustration with fits to current fashion for racers. He is proud of his beach cruiser fits and does them for free, same as it was when his father did them.
Asking a fitter to practice medicine is asking a lot. Not a good position for them to be in. If your current fit is obviously causing needless stress they should be able to spot that.. There would be a limit. Just as there is a limit on what you can learn online.
A handful of fitters do have medical credentials. A good fitter will know who to refer you to if that much is called for.