I used to have an issue like 6 months ago were the game instantly crashed as soon as i tried hosting my own games. Adding "-tcp" to the launch options (in steam, not the game launcher) fixed this issue for me. However as of this morning I have been unable to host my own games again. This time with the same result as the other people here, "failed to create game".
I managed to fix this however by removing the "-tcp" launch option I added all those months ago actually fixed this issue for me... No clue of why, but it works now...