@tamas I know it's a year later, but the 24 pair in box four seems to unlock this for me.

If R5C2 is a 2, then R7C1 is 2 because the two cells in C2 can't be. Or because R6C1 is then a 4.

BUT also, R5C7 is an 8, so R9C7 is a 2 and R9C6 is an 8 and R7C6 is a 2, which means R7C1 can't be 2. Oops!

So R5C2 is 4, and that seems to resolve everything smoothly from there as a series of single options.