The Spectator feature cannot work with Bungee servers. BungeeCord will get a update soon, I'm testing a new system for all my Minigames and should be done soon.

• You can now spectate a player using /splegg spectate <player> or /splegg spectate.
  • /splegg spectate will open a menu with all game that players can spectate.
  • Spectating requires the splegg.spectate permission.
• Added a item that will show all alive players in arena so you can click to teleport.
• Fixed a bug where spectators can interact with Powerups.
• Fixed a bug where players are allowed to fly after leaving a game as Spectator.

To make it easier for you, here are the new config options.

• Messages.Spectator.Menu-Name.
  
• Messages.Spectator.Item-Lore.
  • Placeholders: %players%, %minPlayers%, %maxPlayers%, %alivePlayers%
• Messages.Spectator.Game-Name
  
• Messages.Spectator.Menu-Name
  
• Messages.CannotSpectate.
  
• Messages.CannotSpectatePlayer.
  
• Items-Arena-Item.
• Items.Spectator-Item.

If you are getting errors with your items make sure to change the item names according your server version.

An extra to this update, I've changed the firework type to avoid too much lag. Also, now you can disable the firework from powerup if you want (Options.Use-Fireworks).

This is a Minecraft performance issue that can happen in certain client versions.