I see multiple posts about this, so I'll add mine as well.

I was doing a quest that had me chase an enemy into a portal in talador. When I entered the portal I got a loading screen, then "character not found". Got sent back to character select screen, and can't log into ANY of my characters.

Did a full PC reboot just to see if it'll do anything. No luck.

From what I can tell its any time you earn a loading screen that you get booted.. Portals, hearths, Dungeons, logging into the game....