SRFSPLIT fails at small tollerance

[Proterio]

OK here it is: R6 W10

SplitSrf 003.gh (16.5 KB)

Apologies for not including a file with my initial question. I presumed the answer was nothing to do with the underlying geometry and a tollerance problem like this:

EXTREMES (Z) - Plane mystery

I don’t know, tolerance issue maybe. I opened the file in millimeter template with tolerance set to 0.001 and your gh file returns 4 extremes, as expected. [extremes]