My Amazon was working fine a couple of hours ago.

Thanks Stanley good to know.

FWIW - The Amazon Music service on Sonos is all working fine here too in the UK at the moment. Able to browse, play etc.

Thanks Ken I will keep trying to get somewhere with Amazon where I think the problem lies. 

If not done already, maybe check your Sonos and Amazon profile settings are set to your country of residence. If they are different that can cause problems.

For Sonos profile go here:

https://www.sonos.com/en-au/myaccount/user/profile

You sure this isn’t because you need an Ultimate subscription now, instead of just Prime?

https://support.sonos.com/en-us/services/amazon-music

Working fine for me on a “free” prime account 

can browse all my albums and artists with no issues 

Thanks everyone for your advice. Country settings are all fine and I have been using Amazon successfully through the Sonos app until fairly recently when Albums and Artists listings only displayed about half of my Amazon library. Then I found artists and albums were not displayed at all however I’m now back to being able to see Artists displayed up to partially through letter “H” while Albums are only displayed to halfway through the letter “L”. I have 53 playlists which are listed in Sonos/Amazon the same as in Amazon while I have 11804 individual music tracks which are identically displayed in Sonos/Amazon and Amazon. I also have 240 tracks at the end of the track listing in Amazon which say that “the content is no longer available”. Is my library just too big?    

I have been back and forward with Sonos and Amazon for weeks but getting nowhere, they don't seem to have a clue why this has started happening or how to fix it. I have Music Unlimited. 

Thanks again everyone for trying to help, any further advice would be appreciated.