Unable to split open surface

I am unable to split the two surfaces seen in grey by the rectangle (highlighted), I have tried the split, trim, and wirecut tool … nothing seems to work.

I have deduced that there is some problem with the edge of the surfaces, as it works fine when the rectangle does not extend beyond each surfaces edge (they are joined together but the problem still arises if I explode the hull surfaces into individual surfaces), but unsure how to resolve this as I need it to split the surfaces in that location.
splitting problem.3dm (1.2 MB)

Please help

Hi Elisa - splitting seems to work fine here -

Select the larger surfaces, start Split, then select the rectangle as the cutter and Enter.
Trim works as well.



Hi, I’m not sure to understand, your file works fine for me. the only recognizable thing is that your split will touch two surfaces from your polysruface.
is this what you wanted?
splitting problem_re.3dm (1.3 MB)
I basically did like Pascla just described like 12 seconds ago

strange… it does work when its in that new worksession but not in my original model. Sorry… and thank you