Enemy sent me 30++ attacks and I can only send about 10-15 attacks to my enemy?

[Limelite]

I'm new to this forum and I don't know where should I voice this out. So I'm posting this issue here.
Usually I don't like to register into forum, but this issue is making me so furious right now!
I don't know what is going on with the game, I'm in World 24. My enemy could send me 30 over attacks (from same person, but different cities, and 10 over attacks are from the same city, namely "the Chao").
But when I tried to attack another enemy, I could only send about 12 attacks and a message appear "You've reached the simultaneous attacks to the city."

What is this MESS???

[Tooltip]

Sounds like another player is attacking the same city. In Chaos worlds, a city may only have 40 incoming attacks at once.