Apple Music playlists

My playlists have been shortening by themselves. The last time this happened, one list of 300 songs was shortened to 45. A second list of 150 songs was shortened to 17. This is the third time in three months this has happened. It mainly affects songs I purchased through the iTunes Store and songs uploaded from my CD collection. No iOS update has been installed in the meantime. Does this happen to other users? And what could be the cause? It's very tiring to constantly restore the lists.