Sudoku no 632 (Extreme / Unsolvable)

I set out to make an extreme puzzle and asked my sudoku creator to give me several grids all with the same solution. Once it had produced around 70, it came up with this one, which had a Hodoku grade of Extreme (6092):

I checked this grade with Andrew Stuart's grader and solver, which could not find a solution:

I clicked the Take Step button repeatedly until the solution was found and saw that Bowman's Bingo (Trial and Error) was used several times.

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Solving Sudoku no 539 (Now Solved) at sudoku9x9.com/smartsolver.php

I was finally able to solve this puzzle (without brute force) at sudoku9x9.com/smartsolver.php Click on the image to enlarge it and bring it into focus if necessary:

Susu Smitzh sent me the following version on LinkedIn:

Solving Sudoku no 539 (Unsolvable) at www.sudoku-solutions.com

I was able to see the solution at www.sudoku-solutions.com:

...but it was worked out by brute force:

Solving Sudoku no 539 (Unsolvable) in Andrew Stuart's Grader and Solver

This is how far Andrew Stuart's grader and solver got when solving this puzzle:

At this point I used the Solution Count as suggested:

Sudoku no 539 (Unsolvable)

I ran my puzzle creation program and it produced the one below, which has a Hodoku score of 5398. This usually equates to a score of between 600 and 800 in Andrew Stuart's grader and solver so I was surprised when it said it was unsolvable:

Play online 

Andrew Stuart's grader and solver 

www.sudoku-solutions.com 

sudoku9x9.com/smartsolver.php

Standard Sudoku no 463 (Unsolvable)

Sudoku grader and solver

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