I have a bit of information about what happened that may be valuable, maybe not.
At the the time of the first mass forced logout around 2 am Eastern, I (not american) was on the PTS in one of the new dungeons with (1 american, 2 not). I was booted but the other 3 were not. The only addons I run on PTS are Combat Metrics and Wixard's Wardrobe and we were in one of the trash pulls before the first boss.
45 minutes later around 2.45 am Eastern I was back on live in Blackreach and got hit with the second mass forced logout as well. I was not in a group, just running between keeps. Through a livestream I could see that most of the other players in my vicinity at the time remained logged in.
For me this puts to rest any claim that the logout could be caused by the player or any addons. It's entirely on ZOS's side.
Happened again tonight. Just got done listing a furnishings plan in the guild store and was trying to, no joke, log out. Suddenly busy Leyawiin was at a standstill and then got the boot. For curiosity’s sake I tried to log back in, placed in a queue