In a custom mission, 11 players (mostly EU based with sub 50 pings) were freezing on load when the host transferred the mission. We were able avert this by having everyone download the mission so the host wouldn't have to transfer anything. However even then the load time was slow and we noticed that on the clients, we could only see the load progress of ourselves and the host. Only when the states of the other clients became clear after a long wait did everyone get in game. Desync was minimal but clients were not communicating their load state.
We think this is first a data transfer problem from the host to the clients since we were unable to load until the mission was downloaded by all clients from an FTP. Secondly the lack of recognition between clients slowed down the load as no one knew who was in game or not. Even after the host desync passed, several players were still waiting to load. Again, once the states changed for the clients (they went from the hour-glass to blue) we got client recognition all around.