Offline downloads on Spotify

[Manomano11]

Okay so, i'm a student spotify premium user. So a while ago my spotify on my 6s would stop playing downloaded offline songs offline and the randomly change the green arrow to the grey one even in the downloaded songs. I only realized it once i didn't have wifi. So, I re-installed the app and downloaded all over 1000 probably songs back. Okay, so then it happened again. Interesting was that on my offline songs there are 5 songs that are always at the top and the new songs i keep adding come below it. i ignored it, but the offline download issue happened again, so I then re downloaded it. I went to the settings of my phone and deleted the app and started all over again. But today within like 2 weeks of redownloading for the 3rd time its happened again. and most of the songs are grey with every 5-7 songs with a green arrow while they all are supposed to eb green. OK and also, the app randomly stops playing a song, and crashes a lot. I have no update on iphone software, and neither on the app store. I'm very confused!!!!