For the last couple of weeks google+ has been continuously uploading data whenever it can, so 9 GB over wifi and 800 mb over mobile when it ignored the settings.
I have finally found the culprit, a screeenshot on my phone was copied and corrupted into 9 folders under music - like album artwork. I have not manually put anything in those folders, they were created and filled by MediaGo.
So if you see the count of images to upload in Google Photos going up, and Google+ passing huge quantities of data, look for corrupted PNGs amongst your music.
Chris
