I'm also seeing this issue on a server upgrade from 1.11 to 1.12. While eating will temporarily resolve hunger, when I eat, the food item count doesn't decrease. The hunger bar will temporarily fill, but suddenly reverts back and it appears that I've not eaten. This makes the server instance unplayable and is effectively a game-breaking (or at least world-breaking or save-breaking) bug.
I'm also seeing this issue on a server upgrade from 1.11 to 1.12. While eating will temporarily resolve hunger, when I eat, the food item count doesn't decrease. The hunger bar will temporarily fill, but suddenly reverts back and it appears that I've not eaten. This makes the server instance unplayable and is effectively a game-breaking (or at least world-breaking or save-breaking) bug.