existing problem: BV5000 does not switch automatic to 4G net with LTE frequency 800MHz.
The celluar network setting is switched to preferre 4G network !
Even if 4G is available the BV5000 switches to 3G or 2G.
This concerns sim1, sim2 is not tested.
Therefor resulting a further question: is sim2 also capable of 4G ?

a weak 4G signal will make the phone automatically switch to 3G or 2G network.