Problem Switching Between Wi-fi And 3g

[4octavio4]

I have a Mi4 WCDMA with Global developer 6.9.29 and it has a annoying bug. When I am with wi-fi at home and I go out, sometimes the mobile doesn't enable 3g and the 3g only works when I restart the phone or connect/disconnect fly mode.

Does anyone have any idea what happens?
Thanks.