Multiplayer bug "server uses different version of map"

I am having lots of trouble playing with friends in multiplayer. I host a game, and when they connect it says "Server uses different version of map" for them.

We have tried replacing media.zip, it does not resolve the issue. We have tried inviting through steam, restarting steam, etc. We are getting the best success from my friend right click the username in steam, and selecting "Join game" (every once in a while it works).

Thank you!

Yup, the only reliable fix I've found is to have host start the map, load into the map, have the friends join from desktop, and have the host completely exit the program and restart it each time the map is changed. Do not stay in the program and just put up a new lobby. It won't work. Using these techniques, I've never had a friend fail to join.

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