The app doesn’t know that you have a Ticket (presumably Klimaticket Ö) for Austria. 

Grenztarifpunkt – Wikipedia there you find all ticket border points of Austria. Please note, that some times the Klimaticket Ö is valid more than that, it depends from the local Verkehrsverbund. Like with Österreichcard you can only travel till Lindau Reutin, but with Klimaticket Ö till Lindau Insel. Same things in Salzburg area or in Ausserfern. 

Regiojet (not cd/ÖBB Railjet) to Prague or Budapest accept Klimaticket till Breclav and Hegyeshalom and not till the border tariff point like ÖBB. 

Salzburg is a border station, from there it is for the train tariff Germany, but the app has it as Austrian station. You need to add manually the trip in the app and put the station as Germany. But do not do this with an iPhone, because there is a bug. 

The better way was to buy a paper pass and not a mobile pass. 

Be aware. When the train doesnt stop at where your austrian tickets validity ends, you need your inbound/outbound day!

I dont know if this is the case somehwere in Austria, but you stated something in this direction...

it depends from border to border. Between local Verkersverbünde you have to pay from the last station. For international borders from the border station or the virtual border tariff point. Some times you can use with Klimaticket Ö some lines also outhside Austria because they are part of the local Verkehrsverbund, like at Salzburg-Freilassing (only some trains and busses) or to the first station in Italy (Tarvisio, Innichen, Brenner). 

thanks for all your quick replies. they confirm what I was expecting. it’s a pity the mobile pass can’t recognize existing tickets for home (or third) country travel. 

What do you mean? Can you give an example?

If you have a ticket that covers all of Austria and an Interrail, you never need inbound/outbound journeys. You can always add a manual journey when the border tariff point is a virtual one not in a station.