problem with landscape proxy

having frequent problems with s section of my landscape
it is a section / proxy with a lot of actors in it and also a section where the mouse pointer is over much
one time the layer proxy disappeared without me recalling that i had deleted it
i had to recreate that section of the landscape for my character to stop falling through to oblivion
now this time my character and ai pawns could no longer walk over that section of the landscape and i again i had to recreate it to fix it and have my characters able to walk there still
how does one troubleshoot something like this?