@Liverpool20 I have already checked with wifi analyzer and chose optimal channel (1). My old router worked normal on 2.4 Ghz. So i don't this is the issue

I use dual band and 5 Ghz works fine. But 2.4 Ghz is very slow and unstable. Sometimes it works fine but often loses connection (about 5 times in 15 minutes). Sometimes i can't even connect to WIFI....