When the mob griefing gamerule is disabled villagers can't breed.
What should have happened was when food was dropped, the villagers picked it up. (and bred when the player left the room with correct conditions)
Instead, the villagers walked over to the food but were unable to pick it up no matter what. (and as such breed)
FYI, MC-177120 is open.
Thank you for your report!
We're tracking this issue in MC-55218, so this ticket is being resolved and linked as a duplicate.
That ticket has already been resolved as working as intended, which means this is not considered a bug and won't be fixed. Please do not leave a comment on the linked ticket.
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