Why do some songs stop playing and won't load on Spotify?

I found this on a question posted two years ago - I'm having the same exact problem. The best chosen answer was to kill the app and then re-open it. This does not work. I'm getting really upset because I pay $10/month and half of the songs on my playlist stop playing. Help! I'm hoping that since 2011, there have been advances in knowledge as to why this happens! Anything helps. Thanks!

Previous Question:
I just got Spotify and signed up for the $10/month plan that includes the mobile access. I'm somewhat disappointed, however, because the app has a terrible layout that makes it incredibly difficult to find music that you've saved (all you can do is add it to a playlist or create one). But what is most disappointing is that random songs will not play on the mobile app (iPhone at least) but they will play on the computer program. The songs will not be grayed out as unavailable and will appear to be completely accessible, but when you press to play one of these random songs, it will bring up the album picture and look like it's going to play, but never loads the song.

Heres the help link

https://support.spotify.com/us/problems/