Photos not uploading to iCloud Photo Library

My issue is with iCloud Photo Library on my iPhone 6 (iOS 8.3). Works fine for a few days, then gets stuck and won't upload anything to iCloud, which in turn won't show up in the Photos app on my Mac (OS X 10.3.3). Currently it's been stuck on "4 Photos to Upload" for a over a day now. This happened last week as well and I had to shut off iCloud Photo Library and turn back on. It eventually worked, but that was a long painful process because I have 80GB of photos.

It's not a wifi issue either, and I've rebooted the phone as well. I've been on 2 separate very fast internet connections and only used half the space on my 200 GB iCloud plan. I've edited a few photos with Snapseed and Camera+ using extensions – could it be a corrupt photo using a 3rd party app causing the problem?

When iCloud Photo Library works, it's great, but this is the 2nd time in 2 weeks to hang during upload. I wish there was a way to refresh it or force it to upload without turning the whole thing off and on. Anyone else having this issue?