In our Survival realm we have 3 mob farms, (just your standard dark room with water to push mobs out) a slime farm and guardian farm. All farms produced very well (guardian farm produced about 3 large chest of loot every day or two. Since the phase 2 aquatic update v1.5.0 spawn rates have completely stopped and all that spawn now are the drowned. We can set game to peaceful and back to any other difficulty while next to our farms and the will begin to produce for a few mins and then stop again. Drop rates are now maybe 1 or 2 drops in a day.