After downloading Navionics+ chart region, blank gray grid appears with no charts until chart scaling sufficiently reduced -- iNavX on iOS and Android
Article IX14241, February 28, 2018
Zoom into the chart region deeper (two finger spread apart gesture) and the Navioncs+ charting areas display as thin red rectanges; if necessary, temporarily leave the Navionics+ chart, view any NOAA chart's 00000_1 World Chart, then return to Navionics+ to find it becomes responsive to zooming in gestures.
An ocassionally reported issue with displaying Navionics+ charts in iNavX is that no chart detail is presented for viewing.
You may find that you select a Navionics+ chart region but the initial presentation is only a gray blank grid. The problem: the scaling is too large and fails to show even the world background outline map.
If simply zooming inwards (two finger spreading apart gesture) does not correct the Navionics+ chart presentation immediately, do this instead: tap Charts | My Charts select any NOAA title (even if you do not sail in those chart areas), and select 00000_1 World Chart.
Return to Charts | My Charts, select the Navionics title again and enter the desired region. Now you should see a reasonable scale for the Navionics+ chart and you may zoom into any red rectangular area to see chart detail.
Another approach is to force quit the iNavX app and start it up again fresh. Then enter the Navionics+ chart region and it should present normally.