I've only ever known these to fail when you have enlarged yourself, unless you are going to be pedantic and start talking about being faerie fired, or underwater, or wearing gear that impedes sneaking.

I don't really count it if you fail because you are enlarged. That's equivalent to losing concentration on a spell because you are immolated.

The fact is, some skills do not "fail" when perfected. People have to do some sort of resistance check against them if they even get that!