I am getting the warning below after deleting the legacy dashboard.
Note that I do not use the legacy dashboard or any system dashboards at present - so I have no idea what is causing the cloud request as I have not used it for a long time?
Looks like you may have deleted something that uses a cloud integration.
What ever it was is still connecting to your hub from the cloud looking for the deleted app.
Any thoughts what it may be? If so, log on to the offending cloud integration, (maybe IFTTT etc.) and stop it trying to connect to the hub.