I have also this problem, with regular xdcam clips. Clips don't have metadata, only tc and name ....
like " xxx_D03_camA_shot 001.02"
As it's multicam project with a TC lock, resolve seems a bit confuse between CamA, CamB...camC rush without a good metadata
I also read here that black thumbsnails could be a permission problem whith folders!!!
Most of the time if i save project, quit and reload, most of them appears...after i have to make a relink
Any help with that wll be nice :)