One possibility is that the villagers may not be "happy" that they can't get to their workstations. In Silent's farm, he has the workstations right next to the villagers and the wall surrounding them.
You also may want to check that all the villagers are still linked to their beds in the farm. If you have your base nearby with a bed in it, if its too close then a villager may inadvertently link to it. I would also double check that you still have 21 beds.
I think that the bigger issue is that 1.13 might just calculate the village center differently than before. From what I have heard, the intention was to have Pillager Raid spawns completely outside a village and that they wanted a better way to define what a village was. They may have inadvertently tweaked Iron Golem spawning in the process.
I never really got that particular farm to work properly. I ended up ditching the trading hall portion and putting all the villagers in the middle under the platform, making the platform big enough that it didn't matter which villager was the leader.