Good results in Web Search, getting worse in Mobile Search

[bele]

We are redirecting mobile visotors from http://www.1website.com to http://m.2website.com.

1website position in web SERPS is always the same. But mobile search brings less visitors now, 1website is loosing positions there. I know keywords volume is increasing.

What could be the reason?

(m.2website mobile version is high quality and have very good bounce, pageviews, time on site)

[AlanBleiweiss]

There could be many causes, but generally speaking, mobile SEO is constantly changing as more and more sites migrate to mobile.  At a much higher rate than new sites come on the desktop scene.  So the competition is continually growing.  If you have a mobile specific site, you need to understand that you need to continually work on your mobile-specific SEO to deal with that competition, and as Google does more and more to properly identify the best sites to show in mobile results.