I played Monster Boy and while the first few achievements registered, all the subsequent ones didn't, not even the one for upgrading armor / weapons. Finding all 5 bomb truffles? Nah, according to Galaxy it didn't happen.

Thank you both for the reports, they seem to be quite special cases because I have viewed several cases also quite recently of people completing these games 100%, so in this case it could be individual problems, but I'm not ruling anything out. Let's see if we get more similar reports.

Yeah, could be a bug in the current Galaxy version. But it's annoying in any case.
If I really worried about getting a lot of achievements, I would throw a dictionary at support.

Does anyone own Gas Station Simulator? It seems that the achievements don't work. I wouldn't be surprised if they remove this game sooner or later as well, it's missing several DLCs on GOG and it's published by the shady Polish publisher Movie Games S.A.
https://www.gog.com/forum/gas_station_simulator/achievements_were_not_triggered_in_gog_galaxy

For me the Achievement "Who Goes There?" is broken for the game Metro 2033 Redux.

I have tried getting it many times by successfully doing what it requires (wiping your gas mask 20 times), and I even deleted my config file for that game to see if it would make the Achievement register after I did that, but it didn't.

I also don't have any Achievements unlocked for that game, but I'm not sure if that's just because I didn't meet the criteria for the others yet, or if it's because all of them are broken.

And there are also other complaints on the Metro boards on GOG for other broken Achievements for other Metro games.

I've unlocked this one almost a year ago. Since there wasn't an update for the game, I'd say that it isn't generally broken.

I've never been able to unlock it either. I do have some other achievements unlocked in the game, though I don't know which version I unlocked them with.

After so many years, The Witcher 2: Assassins of Kings - Enhanced Edition got achievements!

It was a real pleasure to remove its entry from the Master Sheet!

Firmament just released without achievements. I just checked on their Discord, they said they will add them later.

Thank you, it would be nice if they would keep their word for once.

Of course this does not keep them from demanding quite a lot of money right now. Sometimes I wonder what would happen if I purchased such a game and refused to pay completely until "later". They have no problem with offering us the exact same thing.

Planet of Lana -- another game from my wishlist released with no achievements (25).

That hurts a lot. I have already contacted a representative from Thunderful Publishing who told me they will pass the request on to the game team, but who knows if it will help.