Try serving him very soft foods that “slip” down easily, in order to transition back into the “food in, chew, swallow” mode; you are eliminating the “chew” component to help him get past the food-holding stage.
When he gets over the hump of his present stage by swallowing foods like yogurt, applesauce, etc, progress to slightly firmer textures. By then, he will have hopefully transitioned out of his current “food-holding” stage and will quickly slip back into his old, normal eating patterns.