Failed to login: Invalid session (try restarting your game and the launcher)

So Ive been playing the pixelmon mod 8.4.2 (ignore affect version information) for a little over two weeks now without a problem, but now im getting this message - - Failed to login: Invalid session (try restarting your game and the launcher) - - whenever I try to access a server. It works perfectly fine on singleplayer. I have tried restarting the client
logging out 
erasing all launcher data on computer and reinstalling
trying different launchers
Nothing seems to be working, it keeps repeating the same issue