I have no clue as to why the dev implemented movement speed that way, why is it even necessary for nearly every single scene transition. The blackscreen problem, well you see what happens is the fadeout / fadein command in the game engine sometimes just don't work right apart from many other things. That's why the bug fix was included by the dev, to recall these commands that didn't work.
Also sometime the game itself just does shit without any reason. I don't know if anyone notice but sometime a quest will just crap itself and when you restart it, it just works. Magic
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, that's just how the way the game engine is.
I hope this clears up some of the issues with the game and the concerns with the mod being at fault
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.