I made a villager breeder design by aJackMinecraft on Youtube, and have spent the day trying to get my villagers to start making more villagers.
They have access to food, they have access to beds, 4 in total, 2 freely accessible, 2 beyond a trap for baby villagers, blocked by trapdoors, the beds have 2 blocks at least of free space above them, the farm is on my ecluded island, far from any villages, and pretty distant from my house and beds, and last point, the mods installed only add new jobs for villagers, and I am not aware of any mod that would change base villager behaviour.
From my testing, it's a problem with beds, as once, I placed a total of 6 additional bed in the greenhouse, replacing some carrots, and they actually started making baby villagers, but as I need them to fall for the trap for the farm to keep producing, I can't babysit the farm all the time I need it to be automatic for my purposes, so I scrapped the additional beds.
One thing I noticed about the bed issue is that my villagers seemingly have no object permanence and forget their attributted beds. They generally sleep in the beds made available in the right aisle, but they keep having those green particules whenever they approach either the right or the left aisle.
Additionally, I have shifted many different villagers around (I was changing villagers because the first ones were related, even if I found no reason to believe it would be an issue), and each time if all 4 beds are placed before they have one assigned to them, they would prefer to rush for the left aisle beds (innaccessible because of the trapdoor) instead of the other beds. And even then, they have trouble sleeping in the beds in the right aisle.
One last thing is that I have tried moving beds around (seperating them by 1 block so they are individual), adding beds in other places that the one time it worked, blocking any and every opening with solid blocks, and removing every trapdoors of the trap (except the floor one) and replacing it with a single carpet in front.
None of these operation managed any result.
I am at wit's end.