FOR EVERYONE HAVING THIS ISSUE:
This is an error with the Advocate Network that crashes your game (unlike what the EA support suggests). There is a fix for this, that resets your Network every time you log in;
Open Origin > Library > TF|2 > Settings > Game properties > Launch Options > Type this in : +communities_enabled 0
The is also a custom Multiplayer client, Northstar made by the passionate community that gives you custom skins, mods, game modes and servers. If you're on PC, check it out
Hope this helps, Pilots
