Go into settings, apps, all, click media storage, click clear data. Reboot phone and wait a while before looking at the gallery. That fixes issues with blank or corrupted pictures in the gallery. Maybe that will force it to sync? If you go into what Exodus says uncheck and check Google+ Photos it will also force a resync.
If none of that works download the Cyanogen Gallery app. It allows you to sync Google+ among other sources like facebook, dropbox, flickr. You just click the plus sign on the menu to add a storage location. My stock gallery app doesn't show my google+ anymore. I am on kitkat 4.4.4