We’re all your devices unplugged, or powered off, when you rebooted your router? My suspicion is a DNS change between your router and the Spotify server(s), but your devices won’t pick up that change unless they are off when the router is rebooted (or, in many cases, rebooted after the router is). 

Unfortunately, it’s unclear from your post the sequence you undertook.

The other option is some sort of port blocking software, such as a VPN. Which keeps the speakers from reaching out to the Spotify servers. Unfortunately, we don’t have access to the diagnostic information, so we’re not able to see what error is being generated. So, I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. Don’t post the resulting diagnostic number here, they get sensitive about GDPR.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Hi Bruce,

Thank you for your quick reply. I switched off the move2 and era 100 speakers (2 off), then rebooted by router and then switched on the speakers.

This problem has been happening since the last 2 days only, and I haven’t made any DNS or other network changes. The speakers are very close to my access points and are connected through 5G.
I will submit the system diagnostic later today.

Good luck with your call, after submitting those diagnostics.

As a note, you usually don’t make DNS changes, they happen ‘upstream’ from your router. Your ISP is supposed to feed the router any changes, and the router is supposed to feed those received to your various devices. Sometimes, this doesn’t function properly, hence the reset, so that it does. 

I use manual DNS settings on my router and ISP modem, both set at 8.8.8.8 and 1.1.1.1

It seems to be working OK now. If it re-occurs I will repost with the diagnostics.

Thank you for your assistance.

That’s your local DNS, I was speaking about the DNS servers ‘upstream’ that feed data to your local router. 
 

Glad it’s currently working. 

Hi, 

Unfortunately, the problem is back as of this morning.

Diagnostic sent (taken immediately after the problem occured)

Moderator Edit - Recorded and removed diagnostics number.