I have a premium account and have 3 devices synced. After replacing my phone, I synced my new phone, but it periodically logs out and deletes any downloaded playlists I have on my new phone. Does anybody know how to manage devices?
Best thing to do (although its a pain) is to post on this topic asking for your offline devices to be reset.
Once you do that, a member of the community team will reset your offline licenses, so you shouldn't have anymore issues - but unfortunately, you will need to redownload any offline content on all of your devices.