Podcast app has removed all my subscriptions - why?

I've only just turned on my phone today and - on opening the Apple Podcasts app - discovered that all my subscriptions had disappeared without any warning.

My podcasts aren't synced with my iTunes account, and I had been using the app last night before turning the phone off to go to sleep, so I have no idea as to why all but two random episodes have been deleted.

Is this is a known problem?