There have been many accounts in more "recent times" in the last 100 years or so where Nechung has given mistaken advice through certain oracles, or where there has been certain political disagreements or oracles fell out of favour with the main authorities.
One of the most common and frequently recited examples is how a Nechung oracle supposedly gave the 13th Dalai Lama the wrong medicine, which cost him his life. Apparently, it was suggested that this oracle was instigated by the spirit of a tulku who had become harmful.
Then again, can the dalai lama really just be harmed by some wrong medicine? Chenrezig can die simply by some wrong medicine? It won't make sense to say that. Leads to another loophole. It does seem something strange is going on that perhaps only dalai lama, nechung and dorje shugden might know about... maybe it could be something that deliberately leads to the "downfall" of Nechung and the subsequent rise of Dorje Shugden. Worth thinking about anyway.