I was using a guide to get all the treasures and by the time I finished S3, the counter is at 59 but all the treasure markers in the level select are filled. Is there something I missed or is my save file screwed.

I talked to every NPC every time I encountered them following the guide but it did not unlock for me. Is it bugged?

When replaying the level "Fire halls" through the level select, the cutscene in front of the large painting does not play and the red key (and enemies) does not spawn making progress impossible.

Does anyone know what the ´´Completionist´´ achievement is unlocked for? I originally assumed it was just for collecting all the other achievements, but I just did that and it didn´t pop.

So, I am in a level where there are a lot of green cubes and there are many red, blue, green doors, but I can't find the key, and I have been through the level a bunch of times. It's that level with the corridor and statues on both sides and there is a teleport near one of them....