So apparently the test app google assistant integration expires every 30 days and testing needs to be manually re-activated as described below. Has anyone figured out a way (short of subscribing to NabuCasa) to schedule an automatic update every 25 days or so, before testing mode expires…???
Syncing may also fail after a period of time, likely around 30 days, due to the fact that your Actions on Google app is technically in testing mode and has never been published. Eventually, it seems that the test expires. Control of devices will continue to work but syncing may not. If you say “Ok Google, sync my devices” and get the response “Unable to sync Home Assistant”, this can usually be resolved by going back to your test app in the Actions on Google console and clicking Simulator under TEST. Regenerate the draft version Test App and try asking Google to sync your devices again. If regenerating the draft does not work, go back to the Action section and just hit the enter key for the URL to recreate the Preview.