Are the chests bugged?

[Taiga]

I'm using a guide to not miss any chest for the achievement, I double check and "talk" to the chests twice before moving on just to make sure everything's fine. But since the end of chapter 2 I've noticed some chests are not counting towards towards the achievement. Like, before going to the school and doing the play, I had 59 chests, then I got both in the old Schoolhouse but one of them didn't count despise me talking and checking them 3 times. Ended up with a chest count of 60 instead of 61, now in chapter 3, after arriving to the city I opened all the chests and that got me to 68, I have opened 5 more chest now, also triple checking them and the count towards the achievement is only at 71, meaning only 3 out of those 5 have counted towards the achievement,

Am I doing something wrong? some chests just straight up don't count for this? (I know story related ones don't count, but I doubt the random chest under a tree I found count as "story chests") or they are just bugged?

[Berahlen]

The chest achievement is slow to update, and I've had it miss one before until I loaded an old save to poke them again. Best to keep an extra save in each chapter just in case.

[Pafti]

There are 164 chests, but one of the ones in the Rolent Sewer at the very beginning counts as "Story Related" and isn't a part of the Achievement. Every other one is required and not bugged.

This guide is invaluable as a sanity check when you fear you may have missed a chest somewhere. But keep in mind that it counts that Story Chest, so when the guide says "140/163", it's actually "139/163" or "140/164". Basically you're always supposed to be one below what that guide says once you're out of the Prologue.
https://steamcommunity.com/sharedfiles/filedetails/?id=295517181

The Achievement tracking doesn't update reliably whenever you open a chest. I don't know the exact inner workings, but the following explanation is close enough to the truth of it, just don't expect it to be 100% accurate.
Whenever you open a chest, or do anything that Steam Achievements track progress for, the game would have to send that information to the appropriate Steam Server, if you open 10 Chests in the space of a minute or two, and possibly collect some Armor or Weapon that is also being tracked for another Achievement, then the game would have to keep sending updates to inform Steam of that progress, when it would be much more efficient to just hold off until a certain amount of progress was made and send all of that information in at once. I expect that, for DDOS protection, the Game will send an update whenever something worth reporting happens, and afterwards locks you out of sending updates for a certain amount of time, maybe 5 minutes. During that time the game still collects all the information to be send out in the next update of course, which will happen when the next update would ordinarily happen after the lockout is over, so say 7 minutes passed, but you didn't do anything worth sending an update for in the last 2 minutes, then it won't have updated automatically, you still have to do something like reading a chest again to make it update. Probably.
It will also force updates when you exit the game, and possibly when you start it, regardless of whether you're supposed to be locked out. With any and all updates, it's still possible for server errors or whatever else to occur, maybe an update will timeout and get skipped. But whenever an update does go through, it will have all the relevant information so you're never losing anything. It just doesn't necessarily show it immediately.

You have 1000 saveslots, so just keep using a new one every time you save after making more than 10 minutes worth of progress, so that you always have options to go back and fix something when you mess up.

[Heroshi]

Do what I did and make a save at every single chest, might have been a bit excessive, but it let me go back and redo every chest when it didn't trigger.

Like others have said though, it's slow to update, so it might be counting but not actually pop up yet.

[SokBritish]

It happens to me too right now. At the end of chapter 2 (after collecting 2 chests in Jenis), I only have 60 chests in my achievement progress. Aaaaarrghh