In terms of why that section of track (the bit going towards the wicker man structure for the first time) is (or at least was) so problematic; I might have suggested this before, but I have a theory.
You may remember that the profiling of that section was originally intended to be very different, and it is only the way it is because John Wardley amended the track profiling very late on in development. However, John himself said that the foundations had already been designed by the time he was called in and wanted to make amendments, so there isn’t much he could do. So my suggestion is; as much as John’s amendments most probably improved the ride experience, is it possible that the sections of track after suffered adverse effects due to them undergoing greater stress than was originally forecast?
He’s said himself that he physically couldn’t change the actual layout anywhere, merely the profiling, so is it a possibility that the additional speed gained from the reprofiled drop meant that the stretch afterwards underwent stress beyond the originally anticipated limits?
There would certainly be a precedent for this kind of thing happening; I once heard it said that the reason for the jolt in Saw’s first drop was because that element was originally designed to only be 97 degrees, but Merlin wanted it changed to 101 degrees late on in development to claim the record for world’s steepest free fall drop. However, they did this without changing the profiling of the surrounding elements, which is why it jerks so suddenly into that first Immelmann.