Default [SOLVED] Photo Auto Backup stopped working

This isn't exactly an SGS5 issue because auto backup was working fine until last week.
But I noticed yesterday when opening the Photos app it was telling me that Auto Backup failed; when I click to backup manually it just sits on pending.
Any ideas on how to get it kickstarted again? Reboots have not helped.

EDIT: I'm lazy and post here before I do much of my own troubleshooting. I scrolled through media and noticed that Photos showed 3 items with no thumbnail and the message Media Not Found when opening them. I disabled Auto Backup, deleted these items, emptied trash, force quit Photos from task manager, cleared Google+ app cache, opened Photos and verified bad files were no longer present, enabled Auto Backup again which claimed everything was up to date. Then took a test pic and it was backed up successfully. No clue what those weird files were but they clearly broke auto backup from processing new content until fully removed.