I spotted a few more games with Galaxy achievements in the database but not active.
Paws: A Shelter 2 Game
Saints Row: The Third
I may have missed Paws: A Shelter 2 Game the first time, but the achievements for Saints Row: The Third were added fairly recently.

Great, so it looks like they're at work to finally add the achievements! In fact Deep Silver has added the achievements to the Metro series, so it makes sense that they want to fix all their games.

Yesterday origins run immortal run achievement has been fixed

Thank you, Yesterday Origins removed from the list!

Code Mystics have replaced the Dotemu version of GAROU: MARK OF THE WOLVES, added new achievements and removed the "All Characters" achievement on both Steam and GOG, so I removed the game from the list.

Remember that to get the old achievements you need to play the old Dotemu version.

Hi, Raiden V: Director cut has a problem with the achievements ???. I think I read that there were two or three achievements that didn't work.

I don't know if that's true

New achievements for GAROU: MARK OF THE WOLVES that added from Code Mystics doesn't seem it not unlocked. Played and beat Terry Bogard Story Mode without contine 3 times and 2 achievements still not unlocking. The Steam version fine, it the GOG version that is problem.

Thank you for the report, I haven't found any evidence to back up this theory at the moment, but if someone else has run into these bugs, we'll find out sooner or later.

Thanks, could you try to contact Code Mystics? They're pretty active on the game's Steam forum. I'm sure they can fix the problem quickly.

Another small update

Commandos 2 - HD Remaster
Victory
I sent the ticket but no response so far.

Dusk
True 100%
Don't Drop It
They should be fixed in recent patches, but it does not seem to be the case.

Styx: Master of Shadows
Passkey
Expendable
Army of clones
Unquenched thirst
Sticky-fingered
Born in the shadow
Outstanding duelist
Serial killer
Sudden silence
Sharpshooter
Sent the ticket, no response.

22.02.2020
Small addition

Styx: Shards of Darkness
Master Goblin

What the heck is going on with all those 100% achievements being bugged on GOG?!

Thank you, I'll wait a while to see if they fix the bugs before adding them to the list.

In the meantime Kalypso Media Digital has answered me saying they will investigate the various bugs I have reported on their games, let me know if you see any updates or changes in the next few days/months/years. I think it doesn't hurt if you report again the bugs as soon as you can, the more people do it, the better ;)

Caladrius Blaze is no longer broken. I unlocked the last two achievements an hour ago and acquired 100% completion, so that game can be removed from the list.

I had problems saving unlocked dual conversations and gave up trying to solve it, but that has nothing to do with the GOG achievements.

Whoa, that's a great news, thank you!

Kevin, I tried to start my game to see if it unlocked and I couldn't! If you made it and I didn't, even though I did all the requirements, I'm thinking there may be a problem with my save.

Could you be so kind as to share your Caladrius save with me so I can test it on mine?

Sure, here you go:

https://anonymousfiles.io/6P1TyM33/

EDIT: Added Patias as friend so we could investigate the issue privately without further derailing this topic. Retroactively unlocking the achievement worked after putting the savefile in the correct directory.

Kevin, thank you very much! Unfortunately you are not recognizing here. I put the file inside the Caladrius folder but it is not recognizing. Did I do something wrong or did the file get corrupted?