Here:
https://youtu.be/UoTX2u3ggvM?t=44s
and here:
https://youtu.be/UoTX2u3ggvM?t=7m5s
In those 2 situations skill landed but expired before you attacked. It last 10 or 15 seconds, not 30. It's very useful if it lands, since you can attack 2 rounds without having to worry about enemy attacking you, maybe 3 if you are very fast.
I didn't watch ultimate difficulties because I don't find it interesting watching something, that at 38k power, we are auto battling. (in fact if you can't auto battle them then I can't even imagine how hard farming events must be... Or at very least how boring.)