2 x Era 300, internet connection via ethernet.
Symptom: constant interruption of playlists, albums and artists in AM via Sonos.
Solution that worked for me: changing the DNS server address from the address of the internet provider (Vectra Poland) to the DNS address 0.0.0.0 in the router.

My problems with AM are finally over and I can enjoy Dolby Atmos sound after 2 months of playing with the internet connection, Sonos app, internet provider, etc.
Maybe this solution will be helpful to someone.