Further to Xavier's comment...

All the (relevant) elevation scraps, maps and exports will need to have

-projection [elevation 90]

as part of their definition.

(If you just specify "-projection elevation" then Therion will default to an elevation looking 0 deg, or north for that object)

Many versions back I discovered that the direction must be specified exactly the same way in each scrap, map and export definition, I presume it is still the case.

ie -projection [elevation 90] is not recognised by Therion as the same as

-projection [elevation 090], and so this can be a reason why some scraps or maps are dropped from an export.

Bruce