It's almost creepy...
I actually have this EXACT same problem. All of it. My game's in 1. Friend's is in 3 to avoid accidents. I played through ep 5 and finished the game with no issues (a miracle). Tried to do the same with my friend's save in slot 3, wrong choices. Went back to try to get 4 to properly load up the choices, black screen with noises in the background.
Only difference is I also have another game already in slot 2 so I can't try moving the game save to another slot. I also didn't GET the rewind option on ep 4. Only start, as in for the first time even though he already played through it to the end (had that problem with every ep since 2 though, so used to it).