This will grow and frame entire screen within 2 or 3 weeks probably. This is a "quality problem" but no solution offered so far. But don't worry much: framed screen looks ugly but the phone will work. It's not as embarrassing if you don't show it to anybody
Maybe Nougat makes some component boiling... Well, before admin asks, write when you bought the phone. bvbw and I did in in the beginning on November, 2016. Maybe our phones all belong to some faulty batch.
I have exactly the same problem with one of my two BV 6000:
Bought the damaged BV6000 MTK6755 with foggy display (on the upper left corner) - on 5th October 2016 - from tinydeal.com (european warehouse) - in germany - with SAME build-no. like the users "axium" and "bvbw": BV6000_Blackview_V01_20170223 (running on Android 7.0).
After two month I bought a second one for my father because I was very satisfied with the blackview BV6000. The best overall package I ever experienced - and I have a long experience using outdoor smartphones, starting from a siemens model, to the lifestyle-outdoor model sony xperia,to a CAT B15 (with had not enough performance) and then a CAT S50. The second BV6000, bought in December 2016 from tinydeal, is still working without any problems - and it´s build-no. (V01_20161011) is older/different than the models affected so far.
Please come back to me with an proposal how to solve this issue as a high quality customer focused company.