The basemap seems to work well in the online environment, however when I add it to the offline environment of ArcGIS Pro (2.0.0) via the portal it does not render correctly when the zoom level increases (as seen in the attachments).
Some sort of tile boundaries show up and they can be seen in both map view and layout view.
I have already changed display options but none of them made a difference.
It all goes well up until this extent:
Zoomed in further:
And even further: