Updating backups in iTunes?

[JHZR2]

Hello, was working on backing up and updating my iPhone XS and my wife’s 6S.

Plugged my phone into my 2013 MBP running 10.13.6, and hit sync. My backup updated, and the backup date went from 8/4/19 to yesterday.

Plugged my wife’s iPhone 6s into her 2016 MBA also running 10.13.6, and hit sync. No update of the backup. Had to hit the button manually.

Curious why it’s inconsistent. Would be nice to be able to incrementally update the backups quickly by USB.

Do I have something set wrong on hers?

 

[Minorite]

You mean that it didn't make a backup of the 6s during sync, but backed up manually? Could it be just some UI glitch?