This issue has to do with the 20th Anniversary Update, which unfortunately broke the Lambda Locator's tracker of 45 cashes - it does update when you are in-game, but doesn't save when you exit and relaunch the game later. In the case when you played the game before the update, the tracker will 'froze' on the number of cashes that you collected before the update. For example, in my case, it was 21 out of 45 cashes. In a case if you bought the game post-update, the tracker will never save and will always revert back to 0.

It's theoretically possible to unlock it by finding all the cashes in one play-through by following guides for this achievement, since the tracker actually updates when you are in-game. But I don't really think you have that much time to replay the entire game in one sitting just to find all those stupid crates. Neither do I.

If you don't have time to actually sit throughout the entire game just for those stupid crates, the only thing you can do with this bugged achievement is, unfortunately, cheating.

Using SAM (Steam Achievement Manager) may seem to be a pretty good option, as the achievement will quickly unlock on your Steam profile will no issues. But it will not unlock in the game, its tracker in achievements list will still be frozen and it will appear as locked in-game.

So the best option is to cheat actually in-game. For this, you need a specific map that will unlock the achievement and will update its tracker so that it's unlocked both in-game and on your Steam profile. I'm too lazy to actually tell you how to set it up, so just follow another guide below, okay? It helped me, at least, so it should help you too.

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1896308154