in version 1.14.0 everything was fine, but when I updated to 1.14.1 and checked my mob farm I realized that the bug of the mobs in which they do not despawn had returned. I tried to change the difficulty to peaceful and then to normal but it didn't work, then use the blocktopograph app that allows you to see the entities in the whole map, that confirmed that the bug in which the mobs do not despawn has returned. This bug does not generate new hostile entities near the player. I hope you solve it