Android - video upload fail

I’m running NC 16.0.4 with Android App version 3.9.2
When (manually) uploading video I’m getting failures. Either the file appears to upload but then is not readable or it fails to upload at all (some files upload without problem). These videos were taken using the same phone and vary in size.
This is what I’m seeing the the nc_data directory:

It seems as if the video is uploaded and then processed? The first four files, whilst uploaded cannot be played on the device.
Any ideas as to what the problem is?