The caves are linked by a surface leg across the depression. This leg is flagged as surface. On the 3d file that seems fine, but on the lox file the image shows a defined passage where the surface leg should be.
Loch has always been well behaved for me in this respect as far as I recall I always have 'walls auto' set in my low level survey files, not sure if that is relevant, just a habit I have that could bias my outputs. I will admit to not checking *.lox too carefully until I have a reasonably complete survey and drawing setup. Do you have any scraps defined for the caves either side of the surface leg? Do you have any LRUD data? If no LRUD are all legs collected 'paperless' with splay shots a well? Are you sure therion is recognising the surface leg? (export survey-list etc to find out) These are aspects that seem to impact on some default behaviours of Loch. Bruce