ESO seems to get, at best, unstable if your desktop resolution is different than your "Full Screen" ESO resolution.
(It also will typicall merely ignore the setting and run at desktop resolution anyway.)
Here's an example:
Desktop Resoultion is 3840x2160 (4K).
ESO settings:
SET PreferMaximizedWindow "0"
SET PreferExclusiveFullscreen "1"
SET FULLSCREEN_v5 "2"
SET FullscreenHeight "1440"
SET FullscreenWidth "2560"
In spite of this, ESO will actually run at 3840x2160 instead of the intended 2560x1440.
It will sometimes also cause the display driver to crash and restart (which leaves ESO in a strange state, sometimes it freezes, sometimes the GUI goes away, sometimes it resets the interface scale slider all the way to the left.)
(OS: Windows 10 x64, nVidia v361.43 drivers.)