I've found that shared folders mostly just don't work - others can't see the files I put in there - or at least most of them. I don't know what else I could do. (If I share one file with a direct email link generation, that works, so the files certainly are there.)

Maybe I ran into some undocumented antipiracy feature as they were self made AVCHD videos of a few minutes length.

Google drive on the other hand just works.