Put the summary of the bug you're having here

What I expected to happen was...:
stay logined

*What actually happened was...
i started minecraft and i was logged out and it wanted me to sign in. i click the sign in as jimbo1258 (my ign) and it says: We could not log you back in as jimbo1258. please try to log in again. (invalidCredentialsException: Invalid token.) i then log in. using my username and password and i log in. this happens randomly. i can still log in but it is very annoying to do so about every time i try to log in. this is my first bug im reporting so dont blame me. oh, and i have my account on several computers because sometimes some one else is on the PC. so i just go to another one. also i have a friends account that i use and it doesnt do any thing like this to his. i bought the game so i know the invalidCredentials isnt true. thank you. minecraft is awesome! i dont know how to take a pic of the launcher. sorry

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. start minecraft launcher.
3.