Samsung: Backing up messages fails

I am trying to back up a Samsung S5 mini (SM-G800F, running Android 5.1.1) using either Samsung Kies or SmartSwitch. With either program, the backup stalls for a very long time when it gets to backing up messages. When it finally recovers, it announces that backing up messages has failed (the rest of the items are fine). > The following categories have failed to back up due to an error. > > Messages — Device not responding. Has anyone else encountered this problem? What could be the root cause? Is there anything I can do on the phone itself to correct this, and allow messages to get backed up as well? In the past backup has worked correctly with the same phone.