Having YAML disabled stops me from joining co-op lobbys and stops people from joining if I host. I have tested this multiple times with different mod setups, and consistently, YAML breaks CO-OP for me, while having it disabled allows me to join people.
This is an on-and-off issue for me that started recently, and I thought it had been resolved as of a couple weeks ago, but a couple days ago I tried to play again and was back to experiencing this same issue.

I have tried fresh installs of the game with no mods except YAML, I have tried actually deleting the steam mods folder for MW5 to make sure it's not an issue with an out-of-date version of the mod or something, and nothing I do fixes this. I can only join lobbies if I disable YAML, which is very frustrating not only because I would like to use YAML, but because my co-op group refuses to disable it so that I can still play.

Any advice would be appreciated.