I noticed the problem in my apps on both desktop and mobile. But I focused on what happens on my Lumia 950XL.
1) First I install and open the app when the Internet connection is on, so that the products get registered. Then I exit the app.
2) Next step: I disable the Internet connection. I run the app again, but this time it crashes.
I have this issue with all my apps that I have published on the store and have an active Qt Purchasing. One such example is:
I also reproduced this with 4 different apps of my own. I used UWP armv7 Qt 5.9 RC builds.
Then I checked the Qt Hangman example for desktop:
It too will crash if I follow step 1) and step 2). Sometimes it hangs and then it crashes.