There are often inconsistencies because the app is only updated every few weeks, whereas there are many more updates online. That is also why the app should not be used to plan. The best is to use national planners and apps and the DB website or DB Navigator app for international panning.

Any online planner will be more up to date than the rail planner app. If your journey is in June, then the app will eventually get the updated timetable.

If, shortly before travelling, you still don't find the train in the app, then you can add it manually.

Thank you @rvdborgt . I can find the train ride I am looking for in DB website  and as well as eurail self-reservation page in https://www.eurail.com/en/book-reservations#/. So is it safe to reserve seats now and later add the trip to the mobile app?

Re: your suggestion, “If, shortly before travelling, you still don't find the train in the app, then you can add it manually”. How can I add a trip manually? I thought I only could add trips from search results of the mobile app.

Yes ofcourse you can even load trains manually in the app as the Railplanner of Eurail can´t have all eruopeans trains in the app as not all companies share their data There is at the bottom a link (or a plus) add journey manually :)

If a journey can be reserved, then it is safe to do so. You can also add it to My Trip. Never add a journey to My Pass though before you're sure you're going to use it. because if you change plans and forget to cancel your travel day, then you loose it. I usually only ass journeys to My Pass shortly before boarding.

You can add any train manually and that's a good thing since the planner is incomplete: some countries .are partially incomplete (e.g. Italy, Spain), whereas others are missing completely (e.g. the Baltic countries, Ireland). In the planner results, scroll down and tap "Add it manually”. If it even doesn't recognise the stations, look up a random journey and tap on "Add it manually”.

Depending on the journey, by the way, it may be a bit or a lot cheaper to make reservations via the rail operator directly instead of via Eurail.