iGO shows black screen.

On my OnePlus 5, after update to Oreo the screen goes black when starting iGO.
Installed NextGen and it was resolved, then, on next OS update (Oxygen OS 5.0.4.) it happened again but now nothing helps.
Tried installing from play store iGO World and it works but none of the versions here in the forums works.
Any idea how to resolve this issue?
Changed various display setting (auto and so forth...) without success.
Please help anybody...