You need to make sure that the device has not updated the latest OS that may not have been fully tested.
Navblue will put out emails saying when it is safe to update to the latest OS. That can be some weeks after it's released.
Also, you shouldn't upgrade the app until cleared. Again, some back end tweaks from time to time, mean that your. EFB person hasn't released the load to match the latest app update.
All can be resolved with comms with your EFB team.