Okay, so I'm a lvl 25 Khajiit with lvl 67 sneak. Myself, Faendal and Meeko have pillaged caves, mines and the lot with success forever. They hardly ever ever ruin my sneak. Even if Meeko is barking up a storm and pushing me from behind.
Well, Meeko died ( ) so now it's just me and Faenny. Everything seemed to be continuing as normal and it was kind of nice to not have Meeko around sometimes. But then.. I started to do Forsworn related looting and such. And they ALWAYS see me! I'll be a million miles away, sneaking along some rocks trying to plot an attack, and before my 'eye' even tells me I've been spotted, here they come, STRAIGHT towards me with a sword attack!
I don't undertsand what's going on. Why am I being spotted all of a sudden?????

P.s. im not sure if its actually only the Forsworn, or everybody, but I just confirmed that it's not Faendal giving me away. I left him a couple hundred yards away, and some lady way over in her hut saw my approach from way over on the hill....

If you have muffle or sneak enchantments that together with your perks and skill put a value above 100%, it will drop back to 0%.
That could be the issue.

Also, some enemies, like Briarhearts, have a very high detection level.

Environment is a big thing too. In a dark dungeon you'll be way harder to detect than in broad dayling trying to sneak up on someone who has you directly in their line of sight.