When I drag music files from iTunes (desktop) onto a connected iPhone, many times the files just don't copy to the iPhone - the tracks appear in the list on iPhone, albeit grey and the most-left column is a dotted circle with a to me unknown meaning (it might be a progress bar really...).
iTunes 184.108.40.206 (OS X Yosemite)
You can see some of the files copied, while others did not, in the screenshot:
The dotted circles are in the left-most column.
I'll list some things to rule out:
- Not using iTunes Match.
- I do have enough space on the iPhone. It's a new iPhone 6 Plus 128 GB, with about 60 GB free space.
- I do have "Manually manage music and videos" selected.
- I can copy some files, some files just won't copy. Even in the same drag manoeuvre, some files would copy and some will not.