Broken mob farms

Recently my bedrock mob farms have been broken. I built a creeper farm, but the creepers are not spawning. I talked to someone else with the same build, and he is also having the same problem. I also built a slime farm, but the slimes are not spawning either. This happened in a recent update - the one that changed how achievements looked- The tutorial: https://youtu.be/BQ3yGapdt-w
I hope this can be resolved.