For anyone experiencing issues with huge FPS losses in PVE and PVP, this is what fixed it for me.
My particular issue was with CPU use.
You can confirm if you are having the same issue by opening the task manager (<Ctrl><Alt><Delete> Task Manager) then clicking on the header for the CPU column so that the highest usage app is at the top, then run eso.
My particular issue resulted in ESO running at 95%+ CPU usage which resulted in frame rate drops causing FPS in game of single figures.
The fix for this is to edit the UserSettings.txt file located in \Documents\Elder Scrolls Online\live, double clicking this should open it in notepad.
Run a search (<CTRL>F) for "CORE" this should highlight the line
SET MaxCoresToUse.4 "-1"
The "-1" value represents 'automatically set the number of cores', which in my case buggered fps up.
Change the "-1" to "4" to force ESO to use that number of cores, i chose 4 as its two thirds the number of cores for my processor.
Save the file, close notepad, then launch the game as normal.
This was an instant fix for me running an I7 8700K.
Vinterskald wrote: »edit: nevermind, just saw people are having issues on NA now as well so may just be an ESO thing haha