It’s not always up to date or accurate and never has late alterations due to being offline based on occasional downloads.
Always use local sources as well as the likes of bahn.com for accurate planning not eurail app.
That line isn't correctly shown at the moment on Rail Planner, it should be corrected soon… (I hope)
Use sbb.ch, it'll be more reliable. If the train you'd like to take doesn't appear on Rail Planner until your travel date, add it manually.
EC trains require a seat reservation (for the Italian leg) : 11€ through tickets.oebb.at. Add Interrail/Eurail as a discount and select one-way tickets.
However you can do the route fully reservation-free :
- any train to Domodossola (EC trains can be busy but you're always allowed to board)
- R Domo - Milano Centrale (faster) or Milano Porta Garibaldi (longer)