Summary: 9 x 9 area carrot farm  with 2 farmers close to (<20 blocks) villager trading hall (non can breed in hall as separated/non willing). 1 extra bed placed to put 2 x farmers in carrot farm into breeder mode. 1 x Farmer plants carrots fine, harvests them fine. Other farmer is separated by hopper minecart catching system. Love hearts show, carrots thrown regularly - lovely, an endless lovemaking, carrot throwing utopia. FYI This area is in an active ticking area (or perhaps tickling area )

Until you change dimensions and go to the End, unload chunk, or for whatever reason but suddenly the food exchange stops. The hearts are there but no food throwing so farm breaks. Tried fixing by putting tilled area behind catcher who planted a few carrots so proving they had items in inventory. Repeated until no more planting (I stole his carrots to empty him out). Farm was fixed for a few days. Went back to Nether, End, other areas in my world - farm is broken again. Tried replacing with other villagers and still broken. Not sure of why a mechanic that works so well fails so badly after a while...