Most of this info has been publicly available on the USAF JAG website for some time
here,
UAV "mishaps" form a very large percentage of the total hull losses to the USAF now. Without doing any real stats on it a significant portion seem to be tech failures of the engine/gearbox/prop that would down any single engine type. Question I suppose is would you "certify" a manned single with the same failure rate.
Some good old fashioned human factors ones, "pilot" and "operator" looking at the ground picture as UAV flies into a hill, well we do that on manned aircraft too.
And a couple of UAV oddities, machine takes off in theatre, goes lost link and is never seen again
Probably just skynet hiding its resources.