There is no QR code if you have a paper pass. Then the paper pass is your ticket.

Additionally, always report such incidents to customer service which as many details as you can remember (in any case the exact train):

https://eurail.zendesk.com/hc/en-001/requests/new

Although I have never used a paper pass, I believe there is no reason to show your phone to the inspector if you are using a paper pass. I understand your journey is recorded on the paper pass and that alone is your ticket. The only extras would be copies of reservations on those requiring a mandatory reservation.

I thought maintaining it in the App is simply your choice, although I am confused how you created a trip in the App without a mobile pass to link it to, maybe somebody can clarify for me.

@Yorkie 

When you travel with a paper pass you need to choose if you record your "Trip" manually on the paper pass or electronically in the app. Once you've made the choice you mark that on your paper pass and you can't change your mind afterwards. 

If you record your "Trip" electronically you need to show both the paper pass and the app with the "Trip" during ticket inspection.

It is indeed your choice. You can add a paper pass in the app. In My Trip, tap on the + at the top right, name the trip and then enable "Connect a ”Pass to this trip".

However, given that too many staff don't seem to know this possibility and the fact that app bugs pop up every now and then, I'd just use paper only to record my journeys.

The person in the OP was using the app not the paper travel diary to record their journeys, with a paper pass you can choose to use either one or the other method.

My own take on it is that it is better to stick with using the travel diary with a paper pass.

There is nothing stopping anyone using the app as a tool for personal use but mixing the paper pass and app for official purposes is just asking for this sort of problem with ignorant staff.