What source?

Hi - it is from Spotify, Napster, 

On what speaker are you having the volume issue or is it across all rooms?

How are you initiating the music? From within the Sonos app or the native music service app?

Using Spotify Connect, it was confirmed recently volume normalisation is applied which has resulted in the volume being reduced for the majority of tracks.

Also check that you have not set a Volume Limit on any impacted speaker/room.

it is on all speakers and I am playing/initiating music within the Sonos app.  I will keep playing with it, sounds like it is not some big known issue but definitely one of the new mysteries from the “new app hangover”