In some situations windows can't reconnect network drives correctly, even if there are configured as "persistent". If you use the windows explorer to explore the drives, you don't notice this issue, because the windows explorer auto-reconnects it automatically, when you try to access it. MP doesn't do that and because of that it displays empty folders.
MP should also try to reconnect it.

h4. Steps to Reproduce
E.g.:

1. Pull out the network cable of your server or PC that is hosting the network shares
2. Restart your test PC
3. Plug in the network cable of your server again.
4. Try to access your network drives in MP