I am having the same problem with two different models (links below); they look fine on my MacBook and my PC, but on the iPhone8 (iOS 11.4.1) they look like the texture is missing. Three important notes:
- fairly large models (100k and 179k tris)
- both models have multiple materials
- both are in draft status.
Can you explain this? If you or I cannot fix this, should you add a banner on viewers where this occurs?