Good point, though I think the "more nuanced cases" are very common cases.
The 2010 flash crash seems relevant; it seems like it was caused by chaotic feedback loops with algorithmic components, that as a whole, are very difficult to understand. While that example was particularly algorithmic-induced, other examples also could come from very complex combinations of trades between many players, and when one agent attempts to debug what happened, most of the traders won't even be available or willing to explain their parts.
The 2007-2008 crisis may have been simpler, but even that has 14 listed causes on Wikipedia and still seems hotly debated.
In comparison, YouTube I think algorithms may be even simpler, though they are still quite messy.