Thank you for your report, and I am very sorry about the issue!
Since the new BIMx app on iOS is equipped with a new engine, there will be some difference between the platform (on Android, Web Viewer and Desktop Viewer, the old engine is still being used). I have forwarded your question to our colleagues in the Technical Support team for further investigation. Once I have the answer I will let you know.
The difference in visualization is caused by the new 3D Engine of BIMx on iOS that we released in July.
The new BIMx engine doesn't use the pre-calculated Global Illumination, which is an old method that we used to generate lighting and shadow in the old BIMx (which is time consuming during BIMx model export).
This new rendering method uses real-time ambient occlusion algorithm (GTAO) that is calculated locally on the mobile device. With renewing the 3D Engine, we reached our most important purpose: the ability to open 3D models regardless of their size.
Since this is the first implementation of an innovative new method, we can surely fine-tune it and enhance its visual results. We are currently investigating with high priority what and how should we improve on the rendering capabilities. We are doing our best to implement significant 3D improvements in order to get a more realistic visualization than the previous app had.
Alternatively, BIMx (legacy) is available for free in App Store that has all the popular features of BIMx PRO.
This app uses the old 3D Engine, similarly to the current version of BIMx Web Viewer. It should help to render the 3D model similarly to what you have on Android and Web Viewer/Desktop Viewer. Please note that the legacy mobile app will not receive further developments in the future.
I hope this answers your question! Please let me know if you have any further questions.
So in sum, the new bimx engine opens bigger files, and exports from AC are faster because the new GI approach, but as a consequence, image quality has been downgraded???
Thank you for your concern! It is true that, at the moment, the 3D visualization is not quite good, but there are surely rooms for improvement! We are doing our best to enhance the rendering capabilities for a more realistic visualization.
I am very sorry for the inconvenience, and thank you very much for your understanding!