I'm having this issue, and I'm on version 2.3.0 (10/31/16 update). I've tried unistalling updates & going to what came from the factory on my S7 Edge; choosing to sync only while charging; and turning off sync entirely. I've done all of these in various combinations with both the factory version and the latest update.
I let the app sync all photos on my phone initially, which took about 8 hours and chewed through the battery. But I understand that. Since then I've been uploading old photos from my computer, but that shouldn't be an issue if sync is off. Plan was to upload, then sync everything overnight while charging, then live life on automatic backup. Now I'm not so sure.