I'm at a loss to explain the December date except that it would have been the last time that vnstati actually created those images.
Have you tried to force update (
uf
at the dn-vnstat CLI) the app? Then wait a few mins and run a manual usage update (option 1).
If this doesn't do it, then try the command Jack describes here:
https://www.snbforums.com/goto/post?id=729470. Then wait a few mins and run a manual usage update (option 1).
If the above didn't work, then uninstall the app, choosing NOT to delete the configuration. Reboot, and then reinstall (from
amtm
, just type
vn
and you will be prompted to install). If you want to "belt and suspenders" save your data, please see:
https://www.snbforums.com/goto/post?id=707414. Then wait a few mins and run a manual usage update (option 1).