I guess I am being thick - but where is the black screen on loading bug in that last clip?
From what I saw it was no loading screen at all.
From my own point of view I occasionally get an "empty window" when running some games (not just Sins). It doesnt happen very often and I havent managed to work out what does it (ie I cant make it happen everytime).
My suspicion is that it is AV and the Windows security falling over each other as game is loading. If I right click and close the app from the taskbar (or end the process from task manager if I don't want to wait) and reload it has always worked on the second attempt.
I do not think this is specific to Sins though.
[EDIT] Suppose I should Add - MicroTower - ASUS, quad i5, 8gb ram, Nvidia GTX260 (I think - its been a while since I looked), Win 7 Ultimate 64bit, ESET Business AV/ESET Home Smart (nothing changed when I changed app).
So far this has been an occasional problem on Sins, CIV 5, SWTOR, Dragon Age, Machinerium, and F1-2010 that I can remember off the top of my head.