Thank you for the reports all, these are reports I’d like to investigate further, as your framerate should not drop that low. A few reports did mention “installed all addons from scratch”, please make sure to test this thoroughly without any addons installed. Even if disabled in-game, the addons are still loaded and can cause some odd issues at times. To investigate this throughly, please test with a “clean” World of Warcraft installation. Disable your Addon manager (if you use oen) and clear your UI (addons) completely. Close background applications and see if the same framerate drops happen afterwards.
If that still does not help out, post your System Files so we can have a closer look into this. Please go through the steps listed here, and create both the MSInfo and DxDiag files. Post them on a page like Pastebin.com or share directly with us through OneDrive. Post the links here afterwards as Preformatted text </>, so we can have a look.
Have a few seconds to spare? Let me know how I’m doing!