I'm almost certain it was a Scourge you were fighting. I don't recall the logs ever showing Core Necromancer or Reaper absorbing damage when in Shroud. Barrier, on the other hand, can seem like an ever-present effect depending on your own damage output. If you are spec for survival, your own damage output, whether it is power or condition, may not be high enough to remove their barrier in a timely manner, especially if the Scourge is also spec for survival too. One last thing, the Scourge can only cast 2 applications of barrier while under a hard Crowd Control effect. If not CC, they can cast up to 6 different applications, although most will only spec for 3.