I’ve change the order of new/review cards on PC and after sync Anki on iPad and iPhone show some strange error when I try to study cards. The only way to get rid of this message is to close the app.
Are you sure you are using the latest version of both Anki Desktop and Anki Mobile?
If it’s the case, it looks like a bug.
A fix for this one will be in the next update; in the mean time, you can work around it by adjusting the deck options, and changing the new card gather order from ‘descending position’ to something else.
Yes, I have latest versions on all devices.
I’ve changed settings back the way they were and now the app is working. Not the way I would have liked it to, but still.