I think the never-empty plate is actually empty once you’ve cancelled the stuck eating action and the Sim puts the plate down, as far as the game is concerned, which is why if you direct a Sim to eat it the action drops out of the queue and they’ll never do it - as far as they’re concerned it’s an empty plate even though it looks full.
I’ve found so far that if you get the food out of the fridge and put it on a counter or table, they’ll eat as usual and empty the plate, so it seems to be ‘get leftovers’ from the fridge that’s the problem. I haven’t tried that enough to confirm that, though.
The missing number of days left for food in the fridge is annoying. I’m playing an Apocalypse Challenge and even though I’ve lifted Culinary, under the updated rules there are still some food restrictions and I don’t like my Sims wasting food! It still doesn’t show up when the food is on the counter. It does show up sometimes, though, but I haven’t yet spent time trying to identify under what circumstances. I suspect it’s something to do with being off the grid - I haven’t lifted that restriction yet but am allowed to go on the grid for daily career tasks or skilling so I’m constantly switching between them. The fridge has to have ice added when off the grid and I wonder if the missing length the food will keep is connected to that as well as where it’s cooked.
