Just began happening today. This has been occurring about every 15-20 minutes. I'll be playing in a multiplayer session and will randomly get automatically signed out, then I'll get redirected to a pop-up window where I have to sign in manually, even though it is supposed to log me on automatically.
I've rebooted and performed a hard reset of my router and modem and it still happens. I have no such problems with anything else connected to my home network, including blu-ray players, laptops, phones, and tv's.