Ok, I did not check if someone already brought up the possible connection before:
I just had another Coop where when the banner came up the other party did not click and I dropped back to the Q. After another player joined and we played our match I tried to starta NM match and after I clicked "Go to battle" I had time outs and had to refresh.
I think I had time outs in the past and thinking about it now I am pretty sure there was that mentioned scenario before with Coops not happening and time outs after.
So maybe (I have my fingers crossed, that refreshing is a bit annoying) this helps you to find what is causing the time outs.
Cheers