Please provide your hub model (C7, C8, etc.) and its platform version from Settings>Hub Details.
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I have the C7 updated to the latest version 2.3.9.201 connected via switch on ethernet. I'm consistently getting this error every 5 or so minutes. I've checked other similar threads and nothing seems to work.
Warnings like the one in your screenshot generally come from an outside service that you configured to interact with Hubitat at some point, but then deleted on Hubitat’s end. So now the hub doesn’t know what to do with an attempted connection that’s still coming in from the outside.
Can you think of a reason you would have configured a webhook to touch a cloud endpoint for your hub?
If you can stop the request from its source, the hub should stop generating that warning.