Disable the ESOhead addon. That is the cause of your issues.

A good rule of thumb. After a patch (any patch), disable all your addons, make sure the game works. Then reenable your addons one at a time and look for issues. That way, you can easily tell which addon is the culprit in cases like this. The reaction to this SHOULD be "Aha, <x> addon is causing FPS issues after the patch, I'll go report it to the addon developer"

Remember, addons are user-created and are not supported, so the onus is on you to make sure they work correctly and don't mess up your game.

For an explanation as to what's going on - Addons are written in Lua, as is the rest of the UI. It all interacts. If Zenimax changes any of the Lua system calls (which patches very commonly do - both to fix bugs, introduce new functionality, and keep addons from doing things that are not intended), addons that are not updated to use the updated system calls properly, will generate a TON of Lua errors. Imagine 100 error boxes popping up on your screen every second.

Now, the game doesn't actually *display* Lua errors, so you don't see this happen. But it keeps happening, and that's what causes your FPS to drop.

I had the same problem, fixed it too! Thank you!