Norton Identity Safe (Android app) Vault won't Sync

Hello, for the past 24 hours (at least), I have been unable to Sync my Android phone's Norton Identity Safe Vault.  I have tried Syncing via both wi-fi and 4G LTE wireless, as well as signing out of my Norton account completely (to completely exit the app) and then signing back in (to re-open the app).

When I re-open the app, the error message is, "Sync failed.  Please try again later by clicking the sync icon."  However, needless to say, every time I try clicking the sync icon, I get the same message:

Any ideas what's going on?  I am using an HTC One M7 cell with Android 5.0.2, HTC Sense 6.0, software number 7.18.531.35 (whatever all that means).  The Norton Identity Safe app is version 3.7.3.791, updated on Dec. 13, 2016.

Thank you in advance.