As the title says, there are 61 achievements missing from the GOG version of the game. I've reached "100%" after finishing two levels.

EDIT: The achievements seem to be implemented but bugged? Unlike Galaxy, my profile says the game is 7% complete (implying they're all there) but none of the other achievements are visible.

Is anyone else having a similar issue?

I emailed the developer and they fixed the issue.

While they all unlock, only a handful (the blue ones, I believe) pops up in game via the overlay. The others, you have to open Galaxy to confirm that they did unlock.