Filenames are wrong

After auto uploading nearly 1000 pictures with iPhone 5s 4 pictures have strange filenames. See picture.
Manually uploading same pictures filenames are IMG_number.jpg.

I found also that filesizes are different. Auto upload vs manual upload. For example auto upload file size 1.0MB vs manual upload file size 805.8KB.

What is wrong?
Client version 2.6.0
Server 6.0.9 ce running on ubuntu 14.04 with nginx.
ios version 10.3.2

Still no comments… :-\