I have low fps randomly every once a while.

I installed the game again 2 weeks ago and when I launched it, I started writing down my username and password, but as soon as the dragon in the cinematic showed up my fps dropped really low, like probably 5 fps. I thought it was a bug, logged on one of my characters and even in the game I had the same problem. The following day I logged in again and had no problem, but every once a while this happens and I can't understand why. I tried installing WoW wotlk from different places and on every launcher I play, the same thing happens and it just fixes itself out of nowhere. I know it isn't from the addons, because I tried to launch it without them as well. I even tried setting the max fps in "config.wtf" in the WTF file. If someone knows how to fix it please help me.

Is this happening only in wow? You need to narrow it down.

If it's just wow, it sounds like your game is going in "background" mode randomly for some reason.