I'm on Android, I've met the requirements for accessing the challenge floor: Met Hellhound, completed all of her events for good measure, cleared the easy, medium, advanced and hard floors, defeating Hellhound on the advanced floor, read the invitation for the challenge floor on the city board, went back to the spire,  as usual a guard stops me on the security floor by the stairs to give the memo about the challenge floor on the off chance I didn't hear about it, proceeded up to the rigged teleportation crystal, but it doesn't work. Only gives the option to go back to the earlier floors. Am I missing something here?