The following 3’s candidate grid came up in a recent puzzle after running through the basics. The candidate in r2c2, if false, would reveal two complementary X-wings, either of which would then eliminate the two candidates in r34c6, which is the correct solution. Candidate r2c2 doesn’t seem to fit the definition of a fin, so, short of trial & error, is there a single-digit rule (colors, chain, etc) that also eliminates these three candidates? Probably something simple, but can’t seem to spot it!

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`. . . | . . . | . . .`

3 3 . | . . 3 | . . .

. 3 . | . 3 3 | . . .

------+-------+------

. 3 . | . 3 3 | . . .

. . . | . . . | . . .

3 . . | . . 3 | . . .

------+-------+------

. . . | . . . | . . .

. . . | . . . | . . .

. . . | . . . | . . .