This one felt like the most difficult calcudoku I've ever done. Even with a lot of guessing, I barely made any progress.
I think there were only about 50 solves at the end of day, and it's a non-subscriber only puzzle. How does this rank against other difficult puzzles?

I'll run some numbers and will let you know..

I was one of the many people who failed to solve it.

I got stuck a number of times and ended up running out of time. Mind you, the fact that I spent around 37 hours door to door flying from Dublin to Auckland didn’t help!

I tried it as well and got stuck

main reason was probably that I was doing the mod options in my head,
must have missed some here and there

It is very difficult indeed. My solver has to compare combinations in 6 cages at once to make progress. The issue stems from inherent properties of the low-total mod cages: they have dozens of possible combinations, most of which have different sums and parities. 1mod cages can take on every sum from 3 to 11, plus 13 and 15... this defeats most of the current analytic techniques.

I was able to make only minor progress myself, most promising feature of the puzzle to me is that the bottom-left quadrant (and thus the top-right quadrant) has a big block of cells that total 67 - however the remaining 3 cells can have any sum in the set {6-7, 9-18}!

Initial candidates
The most I could deduce

Intruding 15+ cage cells add to {4-12}, 2% cage adds to {5, 7, 8, 10, 11, 14}, 3% cage adds to {8-11, 13}, intruding 4% cage cells add to {4, 6, 8}. The range of possible sums in the top-right quadrant align too closely with the range given by the bottom-left quadrant so I do not believe any cage sums can be eliminated in this way. There are just too many sums...

Solver output

I was sweating that puzzle. It was a challenge.

I had to brute force the thing, failing several times. I had to go back and make sure assumptions were correct, and they were. I just made mistakes at times. I finished it with about 90 mins left in the 24 hr period.

I am in the same dilemma as Paul. When I travel, this days are a challenge to get the dailies done.

Maybe this 8x8 mod puzzle should be dialled down a bit?

I would appreciate it. I was not able to do the 12 x 12 on Thursday because I spent so much time on this puzzle.

Alright, the code has been tweaked, and starting next month this particular puzzle
(the difficult 8x8 "mod" puzzle on Thursday) should be more doable

Thank you