DDJ-RB sound lag

Hello!

Just bought my Pioneer DDJ-RB and have a few questions. 

I'm using iMac Late 2012 with El Capitan 10.11.6 and Focusrite 2i4.

The problem is when I'm using DDJ-RB as Audio in preferences and Scarlet + DDJ-RB as output (my headphones connected to ddj-rb, speakers to Scarlet interface) I have lagging (some kind of distorted, noisy) sound after a while (3-4 tracks, sometimes more, sometimes less). Changing latency helps, but only for a while. 

If I choose as Audio - Scarlet 2i4 everything is ok with 512 latency. Is it a problem with DDJ-RB and should I check the RCA master output and test the controller's audio? Or it's because of using the ddj-rb and scarlet interface in the same time?

Also I wanted to ask, is it lag or I can't understand how browser worked. When I load track into deck from browser by controller on ddj-rb, sometimes when I push this button again, previous track highlighted. Or sometimes it starts from the beginning.

How I can always continue from previous selected track?

Thanks!