Been through the related threads on Sonos support and I have tried to reset my controller, remove Spotify etc. as pointed out in another thread. However Spotify still drops out randomly… I have now tested with another Music Service. Spotify is having a problem, NOT Sonos - I can listen to radio and another music service for hours without any problems, but Spotify drops the stream randomly. One note though, after my system reset, remove / add Spotify and so on, less dropouts occurs. So some effect but still not good enough. 
Question- this has lasted for a while, like several months on both my systems. It’s now nailed to Spotify having the problem. Question is if you also have the solution?!