Songs from playlists made by Apple Music keep disappearing and redownloading over and over again!

I really hoped that Apple Music would be much better than Spotify and in some ways it is. But where it fails massively for me is in managing the offline storage/playback. The issue I'm having is:

I saved a few playlist made by Apple Music on my iPhone 6. I added them to my music and made them available offline. A little badge appeared in the top right hand corner of the playlist thumbnail and I could see the songs being downloaded. I toggled 'offline only' mode and the songs within the playlist are in my music library. However, when I go back to this playlist after some time, more than half of the songs is gone! While still being in the 'offline only' mode I can no longer see the badge on the playlist thumbnail and when I click the three dots icon I get an option to save the playlist for offline listening... Some playlists are completely empty and I can see them being emptied the moment I go into a playlist - the songs suddenly dissapear and the colour scheme of the playlist turns white. Then, sometimes I can see some of the songs from the playlist being redownloaded but the playlist is not full (some songs are still missing). It's very frustrating because I never had a problem like that with Spotify. I could see exactly which individual songs were downloaded and they never just disappeared. With Apple Music I never know whether all the songs within the playlist were saved because the little iPhone badge appears only on the playlist itself. An example of this sort of playlist is "Calvin Harris - Remixes & Productions" or "Feeling blue under the blue sky". The second one was saved for offline listening and now I have only one song left in it... The first one had only one song left and now the rest has just been redownloaded (not for the first time!)