So, I only have this problem with 1 character, no matter when i queue, even at the exact 15th minutemark in dalaran, or sit at WG and click queue up, when the WG starts, i will not even have a popup that says the WG is full, and i must wait. nothing shows up at all and im just autokicked from WG if im there and perma in queue.
That's most likely because there's too many multiboxers that queue exactly at the start of the 15m timer. Just be in wintergrasp before that and when it's 15m to start spam /click StaticPopup1Button1. Multiboxers use it to accept queue as soon as it pops.