Use the objective for your version
The objective is to complete every map on the Atlas. In 3.28, only 10 Unique Maps are needed for the separate Atlas passive-point reward; neither that reward nor a displayed bonus-completion total proves that every achievement condition has been met.
A 3.28 report was resolved when two players found they had missed Untainted Paradise. Treat that as a diagnostic clue, not a complete predicate. Grandmaster remains a separate achievement for Hall of Grandmasters, and we have not independently confirmed whether Hall of Grandmasters is also required by Atlas of Worlds.
Build a reproducible checklist
Record the maps you have not completed, then distinguish a completed map from a bonus objective. Note any unusual encounter you tried and whether it changed the achievement state. Use the tracker’s notes for your character.
Before spending currency on a difficult completion, check current official bug reports and the in-game achievement text. If the result still contradicts the objective, include your completed map list and game version in a report.