It appears that Xcode and Reality Composer pro have inconsistencies with RealityView. I noticed that you can switch USD variants in Reality Composer Pro but those are not available in RealityView (I really wish variants were accessible/selectables since it's one of the best feature of USD for delivering assets with variations efficiently). Also I've seen the same issue with texture missing in RealityView from USDZ files that works fine in MacOS, iOS and usdview. I've not verified it yet but it may be related to encoding texture paths in variable in the USD file. That used to not work in MacOS until Sonoma.