as a fellow mom of a 12 hour night sleeper first I'd like to say way to go

You've done well with his sleeping.
Now to the problem at had, I think you'll need to watch him. He may be in fact reacting to the missing dreamfeed, how long has it been since you stopped??
When you hear him in the night, is he crying at all? or is it just moaning?
If its just moaning then he's likly just entered a light sleep, especially if he's resetling into sleep.
If your concerned about it you could try going in quietly and placing your hand on him to help him resettle, or leave him be.
Going in may wake him up, and that could make him grumpy. Or you could go in and he's settle better and sleep better.
Or leaving him may been a restless sleep, or it could give him a chance to learn to self sooth.
In the end, as little help as it is, the choise is up to you. You know your baby. Do what you think must be done.