As per the request in the other thread, this problem has been going for me for a while now:
I spoke to Spotify Support and they had me test using their test account, and the same problem happened. So it's an issue with the app rather than my account.
The only other incidental thing is that I've noticed Spotify doesn't like it when the network isn't fully available: if I try and play music when I just get in the lift, when my phone thinks it still has network connectivity but it doesn't, then Spotify will refuse to play music until it's able to talk home to the servers. I had wondered if this was similar, as the random stop issue seems more prevalent when my coverage isn't perfect.
Spotify Support tried to get me to disable battery saving features but stock Android doesn't have the option to control this.
Update: I've just returned from a business trip with several long flights. Spotify didn't pause once during these flights, which rules out that this is a process issue (i.e. not Android being clever with killing off the process in the background to save battery). My phone was on flight-mode the entire time and it didn't happen, but when I got back to London and got on the London Underground, it happened when the train left the platform and the WiFi connection wasn't reliable. Hence suggesting that this is a problem with Spotify dying when it can't phone home to report on my listening/whatever.