Unable to connect to the server. Please check your network connection

This thing pops up every now and then at complete random. Been playing for weeks/months and the whole night with no problem and suddenly after champ select this ("Unable to connect to the server. Please check your network connection and attempt to reconnect to your game") pops up and I cannot reconnect to the game.

This does not happen on any other game and all websites/web services work perfectly except league of legends. It is obvious that this is quite common as well as I have found many threads on this topic and not a single word from Riot except "send your logs and check your DNS/IPv6" and so on. This is not a client side problem, it is very obviously a server side problem.

It seems that WTFast works to temporarily solve it but it is a paid service, only a trial is free. Very much looking forward to a solution to this because it has cost me not only time waiting for games to end and undeserved queue-delay, but LP and promo losses in the past as well.