The missing floor at First World Hotel, Genting Highlands

On 22 May 2017 (Monday), I took a lift at Tower 1. I noticed that 'Level 21' button is missing.

Out of curiosity, I get out of the lift at Level 20 and went to took the staircase to see if the Level 21 is really missing.
   

Yes, indeed the Level 21 is missing! Why is the management want to remove the Level 21? What is the mystery behind it? Nobody knows. It's really spooky when I was at the staircase.