I had what I think is a common issue when I enabled IPv6 on my router. Pretty much everything worked fine but my Google speaker just kept saying there's been a glitch. Also when I checked the Google Home app they were offline. I know some folks are disabling IPv6 but this is pretty drastic. I found my issue was to do with how the DHCPv6 server was configured on my home router. Checking the settings showed a setting for "Management" with two options: SLAAC (stateless) & DHCPv6 (stateful) SLAAC was the default. As soon as I changed it to DHCPv6 The speakers sprung into life and showed up again in Google Home. This was for a Draytek 2866 router, YMMV, the setting may also be called something else but the key takeaway is to check your DHCPv6 server settings and experiment.
