When faced with this sort of situation I normally revert to the most basic of commands “Alexa what’s the weather”. The outcome from this tells me an aweful lot and from there where to start debugging a problem.

I say this as an indication of the system stability; my Sonos system with Alexa has been stable for more than 12 months, so this is not indicative of my experience.

Your problem normally is the result of duplicate IP addresses, constant rebooting of the router can cause this or a Skill authorisation issue.  I have included my detailed instructions to resolve the majority of Alexa issues below.

Sorry for the long post but this type of issue is normally down to one of three things:

1/ Duplicate device names - Alexa prefers that names for Devices, Groups and Scenes are unique,
1.1/ Please open up the Alexa App>Smart Home and make a note of any duplicate device names;
1.2/ You can then change them in the source app. e.g. Use the Sonos App to change the name of Sonos players. (I personally use the naming standard Room Name + Device type. e.g. Kitchen Sonos, Kitchen Echo Dot, Lounge Sonos, etc)
1.3/ Once you have changed any duplicate names then please In the Sonos app, select Settings>Room Settings and for each of the Sonos One's sign into 'Voice Services' and select 'Remove Amazon Alexa from this Room';

1.4/ In the Alexa app, select the Alexa Icon in the centre of the row of Icons at the bottom of the screen and ask ‘Alexa, Discover Devices’.

1.5/ Here is a link to my naming standards: https://en.community.sonos.com/amazon-alexa-and-sonos-229102/best-practices-for-naming-of-devices-6819283/index1.html

2/ Some form of Account Linking or Authorisation has not completed successfully. There are a number of causes for this and it's best to try these steps 1 at a time and test before moving on to the next step if the problem persists:
2.1/ Open the Alexa App>Skills>Your Skills>Sonos and 'Disable' followed by 'Enable';
2.2/ Ensure that you don't have multiple Amazon accounts logged into different Apps on your device, as this can confuse the Amazon Authorisation. If yes, then please log out of the other accounts and then complete step 2.1 again;
2.3/ If the problem still persists, please logout of all Amazon accounts then select the Alexa App>Skills>Your Skills>Sonos and 'Disable. Now power down all Sonos devices for 10 secs, allowing for any wired devices to boot before booting the remaining Sonos players. Now log back into the Alexa App>Skills>Sonos and 'Enable'

3/ If the problem persists then an entire reset of the Authorisation & Account Linking process is required:
3.1/ In the Alexa app, select Skills>Your Skills>Sonos and then 'Disable';
3.2 In the Alexa app, select ‘Devices>All Devices'. Now select each Sonos Device in turn and click the Trash Can in the top right of the screen;
3.3/ In the Sonos app, select Settings>Room Settings and for each of the Sonos One's sign into 'Voice Services' and select 'Remove Amazon Alexa from this Room';
3.4/ If you have any wired Sonos devices, please power down for 10 secs and then switch on and wait for it to boot;
3.5/ Now power down all other Sonos Players for 10 secs then switch them back on and wait for them to boot;
3.6/ In the Sonos app, Select Manage>Add a player or sub' and add the Sonos One's again. This will complete the set-up process again;
3.7/ In the Alexa app, select Skills>Your Skills and ensure the Sonos skill is 'Enabled', if not please 'Enable';
3.8/ In the Alexa app, select the Alexa Icon in the centre of the row of Icons at the bottom of the screen and ask ‘Alexa, Discover Devices’. Ensure that your Sonos One's are displayed correctly and not shown as 'Off Line'.
3.9/ Also check one last time that there are no devices with the same name. Remember, if there is a need to rename any then you'll need to carry out step 3.8 again.

Let us know how you get on.

@SkiBuddy Without meaning to sound flippant, if I ask Alexa for the weather report, she responds with a weather report for the device’s location.

@UKMedia100% Kudos to you for such a considered and detailed response. Thank you :)

Your first paragraph regarding router rebooting/duplicate IP addresses was of immediate interest. Hopefully I don’t come across as arrogant by admitting this on here, but in a not-too-distant past life, I was a third line Network Engineer, so this is right within my area...

I have a business class fixed and wireless network setup at home (Virgin Media’s “superhub” is just in modem mode), which is even protected by a UPS to smooth-out any occasional power blips. The first thing I did to troubleshoot the issue was look at the Sonos One’s 48hr statistics on the WiFi event logs, and nothing seemed untoward there.

I definitely don’t have any duplicate IPs on my network, but something I might try is reserving an IP on the DHCP server for the Sonos One if you’re aware of any examples where receiving a different IP address from DHCP at renewal time occasionally causes an issue?

Your “point 1” about duplicate devices and naming conventions is quite easy to respond to. The only Sonos device I currently have is the Sonos One in question (yep, just dipping my toe in the Sonos world at the moment...), and it’s also the only Alexa device I have. I simply picked “Kitchen” as the device name to keep it standard/simple.

I’ve been through the steps you listed in “point 2”, so will see how I go. “point 3” I shall keep in reserve unless I need it.

I’m really hoping this is ‘teething problems’…

PS: In my experience, red wine always helps! :-D

Not flippant at all, the fact that Alexa responds with a weather report means the device has managed to connect back to the Amazon Servers, decode the instruction you gave, looked up the weather for your device’s location, and then responded back to the device to play the weather report for you to hear. This means that there is internet connectivity and that for the weather skill at least it is all working fine and dandy at the backend too.

Based on the above being successful, as in your case, then it implies there could be a specific problem possibly between Amazon and Sonos. When you ask Alexa to play music it goes via a bit of a circuatous route: Sonos Device → Amazon Alex → Sonos Servers → Sonos Device. This then links into @UKMedia recommendations above about Account Linking and Authorisation problems.

This has been known to cause problems with a lot of users and personally I reserve an IP address from the upper end of my DHCP address range.

This applies to any Alexa device, not just Sonos devices - not sure if you have any Groups or Smart plugs set-up?  As per my link to naming standards, I recommend calling Sonos devices by the standard Room Name + Device Type. e.g. Kitchen Sonos.  This means that when Alexa creates an Alexa Group called Kitchen (the location) and adds the Sonos player to it, the names remain different.

Always! :) 

Just wanted to give you both (and anyone else who may happen to stumble upon this thread) an update…

Since last writing (About a week ago), the problem has only cropped up once. This time, instead of powering off the Sonos One, I used the “Alexa, stop!” command, then repeated the original “Open Radio <station name>” and it kicked straight in - a much quicker/more acceptable workaround, which if it’s only rarely needed, I can live with.

Before I try anymore tinkering, such as the DHCP reservation or tweaking the name (I like @UKMedia ‘s idea of putting “sonos” in the name), I’m going to run with it for another week or two so that I can get a better understanding of how it’s performing, and therefore a better understanding of the impact any further changes may make.

Thanks again for the help so far…