Duplicate submission created

1. What is the problem? Be very detailed.
We have now had a few examples where a inspector submits a form to the aggregate sever and multiple submissions is created. All text data in the submissions are the same but some of the images are only present in the 2nd submissions and the instanceID is different between the 2 submissions.

Can this be related to a connection drop while uploading ? My client assures us that the 2nd xml is not present on the inspectors phone.

I am attaching a screenshot of 1 part of the xml where you can see the difference between the 2 submissions. All the tags are present in both submissions. Its just the images that is missing from the original.

2. What app or server are you using and on what device and operating system? Include version numbers.
ODK Collect and ODKAggregate v.1.6.0 on an Amazon Linux server

5. Anything else we should know or have? If you have a test form or screenshots or logs, attach below.