Using Forge v*.81 and have had this issue since *.10, essentially on 1st load of forge using the default Minecraft launcher, everything loads aok and i can join the server i usually play on with no issues, however once i've been on for an as yet unknown period of time, im unable to rejoin without completely closing down the launcher and reloading. The best scenario so far is having been online for 4-6hrs straight to 100% reproduce this issue. Attempting to re-join the server all i get is THIS
Log files show absolutely nothing of any errors etc nor does the log window, so i have no other information to add.