I have found and fixed this bug. iRhino 3D 2.1.8 - with this fix - is submitted to the iOS App Store for review. Unfortunately, review and approval can take days.
In the meantime, the Dropbox app for iOS can be used to load models into iRhino 3D. From Dropbox:
- Navigate to the Files tab and find the 3dm you would like the open.
- Tap the 3dm to view it. Dropbox will say "No Preview Available."
- Tap the Share button (box with an up arrow) in the upper-right corner.
- Tap Open In... and select iRhino 3D.
I apologize for the inconvenience.