What is this bug?

Hello @St0Rmy Welcome to the community.

This level has previously been reported, though not for a long time. The problem with this is that if you play a double colour bomb or party popper to start with you will clear all the keys at once, as well as open all three cages all at the same time. In this case one dragon will drop to replace the licorice beneath it, one will stay above the toffee swirls, but the dragon on the very left will slip down the side to where the keys were. This level has never been fixed to prevent this and King probably don't bother because it happens very rarely and only on a first attempt, so players never get stuck too long on it.

It might be worthwhile complaining to Player Support about this. Send them your screenshot and explain that you paid gold bars for extra moves not realising this was a hopeless situation. They may give you back the gold but unfortunately they cannot reinstate a win streak. To contact player support go into Settings in the game, click on the ? icon and scroll through the questions until you see "contact us" at the bottom.