A few days ago i started to play the modpack Direwolf20 on a server with some friends. Today when i tried to login, first it didnt want to accept my email and password. So i changed my passwort acually a couple of times and it didn't work with any of these. A few minutes of raging after that i tried again and i just worked. So i figured out that maybe the Mojang Servers just have a couple of issues and that that was the reason it didn't work in first place.
Now i could login into launcher and start the game. I proceeded like normal and tried to join the server which resulted in getting the the loging error "Failed to login: Invalid session (Try restarting your game and the launcher)".
Obviously after that i restarted my game and the launcher and tried again, but i still got the error. I restarted my pc and tried it again, but it still didn't work. I reset my router, still didn't work.
I really ran out of ideas and started to try find the same issue online, but i couldn't really find the same issue i had online and a solution for it.
Again i thought maybe its just the Mojang servers and not me, but my two friends had really no problems at all to join the server. I also tried to login on the Mojang website and on the minecraft.net website. Both worked completely fine and i could login. The weird thing i really didn't understand was, that i could login into the launcher, start the game, but was unable to join any server. At this point it just couldn't be the Mojang servers.
I also tried to run a normal minecraft version without any mods, but i got the same error. I tried uninstalling minecraft and installing it again, but that didnt work either.
That's basicly what i did the last couple of hours and i just don't know what causes the error at this point and really need some help.
Would be glad if someone could help here. Thanks

Update:
It seems like Mojang is blocking specific Ip Ranges, which then causes the error we get. To me that's totally stupid, because the "Invalid Session Id" error doens't directly lead to our Ip adress being the problem. Really don't know what Mojang did there, but the only solution for us now is, to get another public ip which works.

Ip ranges which don't work:
102.xxx.xxx.xxx
132.xxx.xxx.xxx
134.xxx.xxx.xxx
160.xxx.xxx.xxx
185.xxx.xxx.xxx

Update: Mojang is finally investigating this issue, check here for updates : https://twitter.com/MojangStatus