So I have this field created for one of my users in which I use matrix. EE is version 2.7 and matrix is 2.5.9 I also use MSM
So, basically there is a grid with 2 columns, one is for names and other is for sound. I upload mp3 file, that works ok, I go to matrix field, click add file, I see it, click save and then file is gone. I can do that forever. Like it does not sees change in value.
I have another entry, where also I have sounds, but that entry is few months old. there i click save, everything stays same. It does not delete values.
As far as I see it, problem is in Matrix fieldtype.