The app is never 100% due to the way it only periodically updates, some routes/companies can only partially show or disappear, more often than not missing trains will be in a later update closer to travel time.

It is always advisable to use local sources or reliable tools such as www.bahn.com for more reliable planning.

If a train you want to take does not show on the app you always have the option of a manual entry.

If you want more specific advice then you will have to provide more details.