We're aware an investigating two separate issues with competitive playlists.

• Players cannot see Arena playlists in the playlist select menu.
  • Workaround: Select your server region and queue into another game mode and leave the match to have Arena playlists available again.
• When queuing into competitive playlists (Arena or tournaments), the queue will cancel automatically.

We'll provide an update to the thread when we have one.

EDIT: We've just released a maintenance patch on PC to address these issues. Stay tuned to FortniteStatus for when the patch will be available on all other platforms.