Same for me with dropbox. When new files synced to server, app upload some other files was synced before.
EDIT: now 13 files uploaded to dropbox from 17:56 to 18:04 .. then instantly continue upload each file again (second) .. and instantly continue upload each file again (third) ..
I must catch console output ..
Edit a day later: I make 2 new photos. All 13 files (which was uploaded thrice one day before) was uploaded again today .. and again thrice.