nomansland in world partition?

I have a problem that I think is related to world-partitioning: I have two adjacent regions loaded in my level, and when I open it for editing a number of assets is not loaded - and it seems that these assets are fully located in the gap between the regions - with no points inside any of them. I can load them (‘pin’ in the menu) but this is just for the session, if I reopen the level again, they are again not loaded. In gameplay, they seem to show up. It seems there is a kind of ‘no-man’s land’ between the regions (the World partition map shows that too). How can I keep them loaded?