could be a combo of all together, while i would bet it is WG server or the way it routes you to the server.
1 of my clan matess gets disconnected every clan night, he is not using mods and his internet is perfect for all other games and to DL WOT within a half hour.
he tried everything possible and it is still randomly kicking him out at the start of the battle.
so think there is not a real solution for it at the moment, you could try a few things but would not make it to crazy time expensive (since it would probably have the same results).