Every now and again, an ITM needs to be forced to redevelop. Not sure why it happens but if you look at the properties of each, you'll see the one that's not nesting does not have a developments tab.
To automate fixing this, you can toggle a setting that forces a redevelopment. So from a script or other API automation, you could toggle a setting like DoubleWall, update the fitting, then toggle it back and update again and this forces the pattern to redevelop.