Mark,
I'm using an Android (two different ones) one is a first version Google Pixel and the other is a Samsung J3
The download starts, completes, and shows as being on the device, but when I try to open it, nothing happens. I refresh the screen and it says the mmpk isn't on my device and redownloads.
If I close and restart the app, the mmpk shows as being on the device, but when I try to open it, it prompts for a download and cycles to the above scenario.
It only disappears when I refresh the app screen.
I can't share the mmpk due to contractual reasons, but I can create a mmpk that I can share to see if the issue can be replicated again the above information isn't enough.