Have you tried switching him over to a good quality dry kibble? I had a dog who would refuse three meal times sometimes but never a fourth. He lived till 14 years.
In your case I would the vet take a look at him and try kibble. If he is healthy and refuses his food, I would not push the issue and not bribe with treats. The more attention, the worse it gets. I would give him 10 minutes to eat and remove the food if he leaves it alone and let the issue rest. Except of course when he is anorexic.
Another take: is he under stress? Day care can be overwhelming. Has there been a change in your family, other dogs etc? Two of mine started to get anorexic when our top dog died and I had a heck of a time getting them to eat for three months.
Deja, GSD, sable WL, female, born 11 / 2013
Cam, Rough Collie, sable, male, born 8/2015