Brand new laptop running Ubuntu 16.10... I've installed Resilio using the instructions on this page https://www.resilio.com/blog/official-linux-packages-for-sync-now-available with no issue.
I have a second drive mounted at /media/tony/ExtraDrive1. I created a folder at that location called MySync. In the Web UI, if I paste /media/tony/ExtraDrive1/MySync into the default folder field under preferences, I get an error "This folder does not exist." If instead of pasting the path, I click choose and navigate the directory tree, when I try to expand /media/tony I get the little loading circle, and as far as I can tell it will never complete (I let it run for at least 10 minutes once).
My assumption was that it was a permissions issue, so I made sure that the group was rslsync for each level (/media, /media/tony, /media/tony/ExtraDrive1, etc.), but I still get the same issue. I also restarted the service after making any permission changes, and have also rebooted at least once since making them.