There is an open bug on this. The cloud connector gets out of synch: see Connection error recovery failed · Issue #134 · openhab/openhab-cloud · GitHub
You don’t have to restart openHAB completely, you could just restart the connector as noted in the bug:
As soon as you bundle:restart the openHAB Cloud Connector Bundle the Cloud again properly registers the instance as online
Yes, this is irritating because it stops Alexa and hits at inopportune times. I hope someone can help diagnose this.