Thanks for your kind words! Yes, we have nearly 10 levels, which will be loaded in randomly.
Since we never had any key-related issues while playtesting (even up to stage 70), could you check if:
A: The last enemy in the stage drops gold,
B: If you kill the laste enemy by sword, you may have already picked the key up at the moment it has spawned (you can see if you have the key via the UI in the top left corner).
Sorry for the problems tho. :(