Off-line tracks keep on dissapearing

[user-removed]

My off-line tracks keep on disappearing . I use an Android smartphone and the off-line tracks are on a SD-card which has plenty of space left . I tried a clean installation many times but that doesn't help. 

This problem exists for many years now, so solve this once and for all Spotify! This is ridiculous and very frustrating. I am getting sick and tired of this. And don't tell me the problem has been solved as you have done the last years!!!

Don't stick your head in the sand and solve this!!