The new Crossfire map doesn’t seem to replace the old version when a client updates their game.
Confirmed from 3 people including myself.
Edit: To give a temporary fix for this, if you experience problems joining a server that runs dm_crossfire, just go to steam\steamapps\common\Black Mesa\bms\maps , delete dm_crossfire, re-join, you will download the same crossfire version the server has.
Edit2: This doesn’t seem to happen to everyone and i somehow believe its linked to switching from the public beta version of the game to the stable one.