Why does itunes metadata get stripped in dropbox? Anyone else have this issue?

I have clients sending me .mp3 music files with embedded metadata they input using itunes. Much of the time the metadata is completely wiped once it gets transferred into dropbox. The client will screenshot to show me it's there on their end. Once transferred and uploaded it completely disappears but for the song name usually. Can someone please help with this? It is becoming a detriment to my business and I'm starting to think I won't be able to use dropbox anymore if this doesn't get resolved very soon.

Wiped metadata includes: Album art, lyrics, composer, grouping, bpm, comments ... pretty much everything.

Thanks!