Not sure if others have had this problem, but I finally managed to complete this game while also obtaining the Chronoscepter, but only 2 achievements actually recorded.

The only achievements that my game+GoG Galaxy recorded are the Mantis and Longhunter boss fighters. However, I should have every achievement except possibly treasure hunter.

GoG devs, any updates on this?

I'm playing on build version 1.4.9, & achievements are not working for me either. I've tried restarting the GOG Galaxy client & beating the bosses again as well as completing the Chronoscepter, but none of them work.

Half of the achievements are glitched for me, but I noticed that 3 of the 4 are uncommon and one is legendary at 0.0, so I'm guessing nearly everyone has had this problem?

All achievements triggered on my first playthrough, except the Treasure Hunter (which is bugged for sure). Went through the game a second time, just to make sure that I didn't miss anything.

I seem to be unlocking them, But i don't see any notifications when it does unlock while playing the game.

I got a trigger for tutorial achievement but not for defeating Longhunter.
I think the achievements don't work if you use a cheat.
Meaning i got 9 lives and unlocked infinite lives cheat and i didn't know that just toggle on and off in the menu is enough to break achievements i think. Gonna try reloading a little back.

Edit: yup reloading a little back and i tried without toggling cheats this time and i unlocked longhunter achievement.
the game does say if you enable cheats that achievements won't work in that save file.
Anyway they unlock normally now and when i reach the trigger for it it shows in galaxy while ingame that i unlocked it.
I did get 100%