Check this post. https://forum-en.gw2archive.eu/forum/support/bugs/Explorer-Achievements-Maguuma-and-Shiverpeaks
You probably missed those. Other than that there is a rocky area in mertrica that you could of missed. cant remember the name but theres no poi in there just a passage.
Check the blurred areas on your map to the wiki maps if you still have some left.