My Basic bypass starts with a resolved 4-fill. Did yours?
The final collapse begins with the value 8 scan resolving the naked pair left from the resolution of 3-fill c2[258].
In the bypass trace, you can discover when the previous 8 clues were found.
That was a very productive 4-fill. Here is the collapse trace, and solution.
Next week, another Kampbelmann Hard, 134, offers a 3-fill among the givens. Take it first. If it does not resolve immediately, you at least get a fill string to help later.
Systematic Sudoku 