I bred 2 villagers by trading, One was a farmer, the other a leatherworker.
I put the villagers into a farm area for the farmer to harvest the crops and breed with the other villager and he will not harvest the carrots. When I throw either of them carrots they do no pick it up. I have not traded with these villagers so I didn't think their slots would be full. But because they cannot harvest or carry food, they will not breed.
Are you sure these villagers are "new villagers" and not villagers from before the update of the new villager breeding mechanics?