My game crashes immediately after I joined!

Check step 3B in the Installation Guide. This is the main cause of the issue.

I keep getting kicked out with the reason - (mismatched mod channel list).

If you join the server and immediately get kicked, it's the modpack issue. If you're not sure, clear ALL of the mods out of the folder and then extract the files again.

I keep getting kicked out with the reason - (internal exception java.net.socketexception).

You have a connection issue. You have to manually check out the steps in this video here. https://www.youtube.com/watch?v=PYGZdKOV2fs