I've been noticing an odd issue with a EM/DA stalker where when I'm trying to set up for AS I suddenly would not be hidden and the attack does normal damage. After a lot of testing it seems that this is due to Oppressive Gloom firing off while still hidden, though it should be suppressed until an attack/etc fires. I have tested this by standing in groups and watching it happen without doing a thing.
I always run with OG on, I have been doing so for over a year on this character and this was never an issue before. It only recently started to show up in the past month or two. I can see in the combat logs that OG fires off before anything else occurs. It appears it's not always being suppressed like it should be. It does not happen 100% of the time, but I would say it's close to 40-50% of the time now.
An obvious workaround is toggling OG on after emerging from hide.