Enderman Farm Glitch?

For some reason Endermen will not spawn in my EnderFarm at all anymore, it has been working perfectly until now, where my drop pad is completely empty at all times. Another strange issue i noticed is when you walk into the perimeter of the drop pad, it appears as if my FOV is automatically increases by a bit, but only when you walk inside of it. I tried googling the issue and so far it seems as if I am the only one with this problem 😛.