I've had this issue since I first started using spotify, so for about a year. When playing songs on my phone, playback will randomly paus itself for no reason. Nothing I have done has fixed it and it's extemely annoying. I have:

- Rebooted the phone. 

- Cleared the App cache.

- Uninstalled and reinstallled spotify.

- Uninstalled, removed all cached data, and reinstalled.

It happens on all connections (mobile data, home wifi, wifi other places). The phone is a ZTE Zmax pro and has the latest firmware and version of Android. I don't have an SD card. It happens on both downloaded and non-downloaded music. It also happened on my old phone, which was an LG G3. 

I really need this fixed or else I may not be keeping spotify. It's too aggravating to have to hit play again 3+ times during one song for no reason.