Hi, we’re experiencing a similar issue since moving to 4.7.
Our character is falling through only a specific part of the Landscape. I tested to see if the retopologise tool was creating areas of bad collision, but that doesn’t seem to be the case.
Resampling the landscape seems to fix the the collision problem, but all of the layerinfo we’ve painted gets messed up, so textures aren’t where they should be, so it’s not really a good fix for us.