I have also seen this problem. It appears to be something to do with how Studio interprets the added symbols. I created a sequence using some of the 3D arrows to point to the important areas.
What I ended up doing to get it to work was to bring the arrows in to the Illustration SBOM. When I did it this way, then I could see them in Studio. I also detected a problem where when I would preview the experience, the arrows would not appear during the animation. However, in the published experience, they are visible.
Thank you Allan,
It seems that Thingworx is getting confused when steps contains symbols because not all the symbols are shown correct that we added into the Sbom.
All symbols that we used in the sequence are shown in Thingworx on top of the 3D model and all in original scale, even if the are re scaled in Illustrate and they have different colors as in Illustrate. Will do some more testing with different models and symbols.