Do the following things and you will likely see your issues go away.
1.) In Radeon Settings / Gaming Tab / Global Settings (top left) / Wattman, down bellow the fan settings, slide the "Power Limit Slider" all the way to the right to it's maximum. This will allow the card to receive more power. Don't worry this is still in the safe limits of the card and is not an over volt.
2.) Windows Power Plan setting to "High Performance" if it is not already.
4.) Disable "Fast Startup" (Windows 10 Only)
5.) Disable all Microsoft Game Features like "DVR" in Settings Game (Windows 10 Only)
You can Google any of these on how to do it.
After this you will have a much better gaming experience with your AMD product, as this fixes about 95% of any current problems.
FYI, I have an RX 580 on a i7 as well and have done all of the above and have zero issues playing BF2
Sorry nobody saw your post earlier.
Sorry, at this time i didn't espect an answer.
Anyway, i tried everything you said, but nothing change, i still have fps downs at mid battleplay. but really thanks for your help!
So sorry nothing helped. I play battlefront 2 all the time with no frame drops on my RX580. Wish I knew what to tell you to do.