I use the phone with a german SIm Card.
When i visit the netherlands or czech republic internet does not work.
Roaming is active. Sim card is trying to connect, but gets no connection.
The sim card itself connects via another device (microsoft lumia 950) with internet.
Any others who also have this problem or a solution ?

Android 7
Blackview-V0.1_20170803_20171011-0929
Security Updates of 05.07.2017

Just refer to this thread
viewtopic.php?f=191&t=328646

This issue has been solved some time ago