I'm not sure I fully understand what you are doing with those two floors - is one the normal floor with a hole for the ladder shaft, and the other the moveable hatch ?
And by "fall through", do you mean just climbing down (or up) through the closed hatch, or actually falling as if the hatch didn't exist ?
If the issue is "climbing through closed hatch", there are a two things you must remember, which might be related to your issue:
- when on a ladder, the avatar doesn't react to collisions. He can trigger regions, but he will climb straight through colliders such as hatches (but there are workarounds, like Er'cana's water tank ladders which have hatches on top of them - these rely on more complicated PRP logic though.)
- "climbable" regions are just a PyPRP shortcut and are meaningless to Uru. What is does, is tell PyPRP to create the two standard "climbing" regions as new objects. For instance, in the next picture, the left picture is what you create in Blender. The right one is what PyPRP would give to Uru.
- Show Spoiler
Those two regions may be quite big (I don't remember how much), which means the avatar might still try to climb on the ladder if he is too close to the ladder region. In which case you'd better create those two regions by hand, and make them smaller (even small regions should work).
Oh, and obviously, using a single region means you can't animate it or disable it with AlcScript, so watch out.
Not sure if that's what you wanted, but I hope that could help regardless.