Darren Branford

I am experiencing this in my world, too. The guardians do seem to be getting stuck on the sides of the drop chute and are seemingly able to travel vertically at will. 

I have also also observed that the guardians lose the ability to cling to the walls whenever they attempt to shoot their laser beams. 

Played on an iPad. 

I can confirm this (was going to file my own ticket before I found this one).

In my case, I built the tower in my single player survival world before the latest update, with every platform being made out of top slabs. It worked extremely well.

After the update, not a single mob will spawn on it.