I have the same problem when i try to play "merc" and dlc's are active...
When searching for a "team deathmatch" or "kill confirmed" it's going beter but still difficult.
I have no problem anymore when I deactivate the dlc's.
What a shame to pay for the dlc's and not be able to use it how it would...!
Maybe it is a bug but I have dlc 1,2 and 4 and I guess it's a problem to find people with the same maps...