I received my BV6000 2 days ago, i'm totally satisfied except the connectivity when on mobile data.
I have experienced no connection from time to time, 6 of 10 attempts, even when i have full signal 4G / 3G.
It lasts for some time f.e. 20 mins and then it comes back on..
I have only 1 sim card in, which is obviously preferred sim for data.
Any help?

try a firmware update to see if problem can be solved.