Despite being tracked in game, the achievements for secret zones and points of interest don't trigger. In GOG Galaxy they are labelled as legendary without any percentage, so I'm guessing they just don't work for everyone. Even discovering a secret zone for the first time is in this situation (the first point of interest is working though).

I have tried a repair / verify game files, no change.

Yeah, I can concur, the same issue here. Tracker for this achievements must be off or smth. Tried reinstalling gog connect, vc libraries, deleting saves and starting over etc. No luck. Then saw that there is no percentage stat for how many people unlocked it so it's pretty obvious that something aint right.
I suggest writing to the devs directly through their mail - contact@fireplace-games.com. That's what I'm gonna do because I don't see much activity from them on this forum.

Thank you for your input Sinsonte! I have just emailed the devs in French for easier communication. I'll keep you updated.

No problem, dropped them a line too. Let's see what happens.

Even the "Interesting..." achievement for discovering a point of interest for the first time isn't unlocking for me, despite having discovered several in episodes 1 and 2. It is labelled as "Common" with a rate of 98.1% in GOG Galaxy, which indicates it once worked though. I've also emailed the devs. Has anyone gotten a response yet?

EDIT: I just tested what should've been a very easy achievement to unlock, "Curtain Call" (Watch the credits till the end.), and it didn't unlock either. Looks like all the achievements are broken.

Nah, It's been almost a month, still no response. What's left? Dunno if complaining on steam forums is worth the shot. By the way, that "common" achievement didn't work for me either the first time around, but after deleting save files and starting over it popped up when triggered. So you can back up your saves and configuration files, and try again with clean start, then after getting the achievement, swap back the old files.

I have the same problem, the challenges and points of interest achievements don't work for me either.

I have the same issue, opened a ticket on GOG, but given that the devs didn't seem to respond back in august, seems unlikely to be fixed any time soon.