I noticed that sometimes, if I play fast, some encounters don't trigger properly.
I thought it was an SCS issue, but I uninstalled SCS, and I still have the same issue sometimes.
I'm playing with an iPad, which means two things:
1) Uninstalling SCS it's easy, I just have to clear the Override (well, in my case the character) folder, so it has been uninstalled properly.
2) IPad 2 it's not very fast, and this could be the problem. Scripts may need more time to load.
It's easier to reproduce if you are wearing boots of speed and drink a potion of speed.
I go where an encounter is supposed to trigger, and nothing happens, but if I go away from the trigger point, and wait a minute, the encounter trigger properly.