if you read the reviews on iTunes, you can see how common this is. it crashes a lot! and with the sample model it comes with, no less. further, $10 for a viewer app that crashes 10 seconds after you open it? there are whole 3D apps on iOS for free that work better.
please, dont take advantage of your loyal customers. fix your app please, especially after you have taken my money.
BTW, on an iPad Pro, so there are really no excuses as to why it doesnt work