OK. I admit defeat. The puzzle has a unique solution. Following my initial attempt which ended in two possible solutions (see other comments), I studied the ears of the jigsaw pieces and suddenly realized that the four ears in the top left must each contain the same number, as is the case for the bottom right four ears. If these grouped ears do not have the same number, then one or more of the jigsaw pieces will contain a duplicate number. Try it yourself. This results in row 4 having to be 978435612. Incidentally, I re-solved the puzzle without using the rule of rounded numbers in the rounded squares or ears.

Guy, Udon Thani, Thailand

If you change row 6 to 936 then the jigsaw piece at bottom middle contains two threes.

Lianna, Sheffield, England

I agree with Richard and Guy. Even with the rounded numbers rule, there are definitely 2 solutions to this puzzle. In fact, the rule narrowed the choices so much that it was relatively quick and easy to solve.

Given that, why didn't the puzzle setters or contest organisers test the puzzle by solving it themselves beforehand?

Or is there another rule that wasn't published online?

Karin Edwards, London, UK

I agree with Richard and Guy. Even with the rounded numbers rule, there are definitely 2 solutions to this puzzle. In fact, the rule narrowed the choices so much that it was relatively quick and easy to solve.

Given that, why didn't the puzzle setters or contest organisers test the puzzle by solving it themselves beforehand?

Or is there another rule that wasn't published online?

Karin Edwards, London, UK

I agree with Richard's first comment. The puzzle can be solved either way with 693 & 936 interchangeable in rows 4 & 6. The rule for "rounded" numbers in the rounded cells does not resolve this.

Guy, Udon Thani, Thailand

Still not sure this is unique ....

Surely the 936 in row 4 is interchangeable with the 693 in row 6 ?

Richard, Chorleywood, UK

Yes you can solve it that way, but the Jigsaw Sudoku has a rule that all the digits in the rounded cells must be "round" numbers (3,6,8 or 9)'. So that make it there is unique way solving this.

Hieu, Newport Beach, CA/USA

Richard, you're forgetting that the regions are no longer 3x3 blocks, but they are jigsaw-piece shaped. For example, you have two 4s in the upper-left piece.

Wei-Hwa, Mountain View, USA

This surely isn't a unique puzzle !!

I have found an alternative solution ( below ) , which itself isn't unique as the 6&8's in col 6 & 7 are interchangeable .

Seems bizarre that a world chapionship should be decided on a flawed puzzle ?

159 827 436
263 451 798
487 639 152

678 245 319
521 396 847
934 718 625

712 963 584
346 582 971
895 174 263

Richard, Chorleywood, UK