The official Halo eSports league, Halo Championship Series, had to cancel the first cup of its second season because, six months after launch, The Master Chief Collection is still broken.
The event was intended to span across two days, last Saturday and Sunday. The first day went smoothly but not the second one when a large portion of players found themselves unable to connect.
We're aware of and investigating party joinability issues. As a result, we'll be canceling HCS Cup #1, and apologize for the inconvenience.
— Halo (@Halo) April 26, 2015
The Master Chief Collection was released in November 2014. The launch didn't go smoothly as the game required a day-zero 15GB patch download which still couldn't allow most players to play online. Microsoft and Developer 343 Industries released several patches to fix the game's matchmaking, ranking, connectivity and stability issues. The last patch was released last week, but it seems that there is still work to be done.