3 times tonight the game switched to window mode. Twice in the middle of a fight and the third was while I was zoning. The game is unplayable like this.
Have you tried just playing in window mode? You are saying it is unplayable but just because you can't play in full screen without it jumping out doesn't mean you can't play in window mode without it randomly jumping back to full screen. Honestly, I am confused when anyone says they play in full screen mode since the window can scale properly now, I only play in max expanded window mode. Do you use 2 computers? Back in the early days in EQ I would only play full screen when I had a second computer I could use on the side for surfing the web to find information about what I needed to do.
I'm having a similar issue (amongst others) just not as frequent. The window may scale for you but for me the window bar is larger than normal, my window (buffs, chat, mercenary, etc) placements are all over the place and putting them back means overlap. Fullscreen mode is preferred and since it was working prior to the DX11 downgrade I see no reason why it shouldn't still be unless they announced it is no longer supported. It is a shame that the powers that be can't listen to the people on the test server when they stated, repeatedly, that the DX11 fiasco should NOT be pushed live.
I don't play on test and I don't know how they decide what goes forward and what doesn't It may be that those having issues is alot smaller than those who are being vocal about it being an issue. If it is less than 1% or less of the players they probably decided that it was fine going forward since only a small number is having issues.
You mean that this happens spontaneously? I suspect you're pressing some Windows logo key combo somehow. Please message me your Logs\dbg.txt file the next time this happens.