Default [Q] Signal / data drops out?

Hello!

I have problem in my Jiayu G4 (MTK6589T), after when I switch from WIFI to data, my signal drops out (not always, 1-3 a week). Manual/automatic search not working, is not available at the moment. Only thing is that I remove battery and placed back to phone...signal is in seconds back...

This problem were the same in factory ROM, and new ROM dec.2013.

Is possible fix data in 3G, I think that is this problem (switching to H, H+...G3...)?

Please for help!