1. Please check that you have the latest app update.
2. Checking timetables is best not done with the Interrail planner app because it doesn't get enough updates to be reliable. It's better to use the operators’ own apps/websites and the DB website or DB Navigator app for international planning.
3. If you tell us which trains are you trying to book, then people can advise you where else you can book reservations for them.

IF you had given more details, it would have helped.

As about any railway changes their timings per 12/12 coming, it may also simply not (yet) be in the system.

And as rian tells: its always best to simply use the planner of the railway concerned, not that of Interrail