Many people have mentioned that their Eavesdropper achievement was bugged, or was inconsistent to unlock. The conditions to unlock this achievement has a caveat.

The problem is that all passengers must have had their last textbox disappear. No other textbox must be allowed to reappear afterwards. If you go back to a passenger, their textboxes will replay, which means you'll have to stay in front of them again and wait until their last textbox has passed. This might be a pain to wait for.

So the optimal plan is to go all the way left, then play the eavesdrops one-by-one, until you reach the seat. Next you go all the way right and eavesdrop one-by-one until you are back at the seat. And sit down.

You do NOT need to quit out of the game, reinstall the game, or anything else. Let me know in the comments if this method has worked for you. Thank you!