When I view a (theatre set) model in iOS mobile viewer (latest version) I get mottled grey/black blocks near some leader text.
Here’s a screenshot
And the text sometimes disappears from view. When I move away from the Plan view to another Scene, then back, often (but not always) no leader text at all is visible. To get it back if that happens, I have to turn the text layer off, then on again.
The black or grey blocks seem to occur only on multi-line leader text, as far as I can make out. Single line leader text doesn’t seem to be affected.
Most but not all of the leader text near the corners of the image has near it black or grey blocks, which seem to be artefacts. They don’t show in SU itself, nor in the desktop viewer.
And here’s a link to the model itself (it’s too big - about 8MB - to upload here).