Hi there and thanks for the extra info
There are a couple of possibilities that could be going on here.
The first is that there is some sort of restriction within the throat that is making it difficult for him to swallow his food, usually though, in these cases, a swelling can be felt, and also upper airway (breathing ) noise will occur due to the constriction, so this is less likely than it being a problem within the muscles of ether the oesophagus (food pipe) or throat, that means he cannot swallow properly- this can be neurological - so related to the nerves that supply these muscles, or primarily a muscular problem.
My advise would have to be to get him checked at the vets, as it's possible this condition will continue to get worse, especially if the nerves are involved, so treatment and investigation may well be required.
In the mean time, i would advise feeding him from a height, so he doesn't have to bend to eat, as this can really help with oesophageal problems, when the musculature of the oesophagus isn't working properly.