Problem with framerate on battlegrounds. Help!

Guys i got a problem. Since sunday morning on battlegrounds my notebook's going crazy. Every time when i met somebody from horde framerate going down to 4,5,6,7 fps and notebook fan is starting work so loud, so playing is imposible... It's happend even on low details. Meanwhile for exemple in dalaran or in wintergrasp on ultra details I got 60 fps all the time.
Notebook:
16GB RAM
i7 9th gen
1660ti
If somebody know what is the reason, please help!

Turn off all the addons and check if it still happens. Then run the task manager and take a look at any processes that may be taking all the space. I've noticed there's a new malware function called "sysmain.exe" that "optimizes" your apps (It doesn't) and usually takes up to 80% of the CPU usage. So try first without addons and then check the taskmanager and start discarding issues until you find the cause.

Hope it helps.