The issue with some achievements not working has been fixed. All achievements should now work as intended, though any progress towards unearned achievements has been lost.
For example; regardless of the number of Official Levels someone has played through, all 25 will need to be completed from this point forward to earn the achievement '25 Revolver'.
Completing the requirements for an achievement in a single session is not necessary.
For example; while attempting to earn '25 Revolver', you can play through the first 20 Official Levels, exit the game, then load it up at a later date to complete the remaining 5 Levels.