mapping bug/problem

im doing work on a set of underground levels so there are a number of blank levels around the map, but my problem is there are a streak of diagonal levels that i have made and filled in that are still showing up as blank when i map them…

of course i have been over there levels names and the .txt file trying to figure this out but i cant see anything wrong with it… and as it is a diagonal line of levels that don’t show up when mapped (a1,b2,c3,d4,e5,f6,g7 and so on.) i don’t think it is likely to be anything i have done, as accidents rarely fall in to such perfect patterns and mostly are more general.

so anyone know what it could be, or have any idea how to fix it?