How to complete the MAM dialect to get 100% completion?

I’ve completed the main story line and returned to all of the maps and finished 100% of the missions and collectibles, yet my overall progress shows as only 98.43% complete in the main menu. When looking at the Artifacts tab, I found that it shows the MAM ancient dialect as only 83%.

How could I have obtained all of the collectibles in the game and not completed the MAM dialect? What did I miss?

100% completed maps are: