Map completion statistics not correct
The Map Explorer achievements work differently to map completion (which is finding all POI, Skill Points, Vistas etc.) The Map Explorer achievements are determined by the number of unlocked white-named areas on each map, like Wildflame Caverns, Haivossen Kenning, Thaumanova Reactor etc.
Therefore, I’m guessing that you’ve completed each map, but on several maps you’ve missed discovering some named areas. Map Completion does not always take you to all of the named areas; you need to use a fully completed map as reference, or just be very thorough in your explorations.
caves with no poi’s are usual suspects