Oh, thank you for taking the time to respond!
Weirdly, though, I've done all those ones already.
.... oh my god, I figured out why. I confused my left and my right. I am so sorry xD
No worries!
- 2nd row, right-most
To get this one check the postcard Polina gave you.
- 4th row, right-most
For this one you need to unblock the "star" button in the elevator. There's a hint on the elevator wall that might help you figure out how to do that.
- 5th row, right-most
You might look for footprints on the snow in Mystery Cave that point to a secret place.