New Summoners Rift Sounds Lag

I tried to test the new rift but a few minutes after the game begins, all the sounds starts to lag and it never comes back to normal. Animations lag too. I know my fps is really low (like 17 in the begining and 03 in late) but this problems don't occur in the normal server. And I hope it won't occur when the new rift comes to normal server.
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