Hello,
I'm new too (45 ladder match played) and I have the same issue.
It's strange as I have a good computer I'm (close to be) always the first in the match page in the game. Then it waits for the last 1 or 2 player to connect and then say that I've caused the matchmaking connection failure.
I also have a stable connection normally.
What can I check more on my side?

It happens every 2 or 3 map I start.
I feel sorry for the other one joining and not be able to play because of my problem.