Hi! I was using fAircrack and noticed a thing: sometimes, when I use Korek attack (aircrack-ng -K), it doesn't work, it stays cracking the key forever, while PTW attack (aircrack-ng -z) works; other times, it's just the contrary.
My knowledgment, in this case, is not so great to understand why, so, I guess you have just to try both methods.

Then, why when a network is hidden, it shows weird channel numbers?

This way, it's not possible to use deauthentication attack to find network ESSID.