Villagers Not Changing Job When Block is Destroyed

Help! My Iron Golem farm is not working because the villagers are not changing jobs or working. Below, I tested it by spawning a villager, making it get a job, destroying and then replacing the job block with another. The villager did not change to the next job and was a novice. I reinstalled Minecraft, but it still did not work. I created a new world, Villagers worked, and then after a few weeks, it broke again. What is going on?