The cause of the error was an outbound firewall rule that blocked access to https://scanner.sonarcloud.io. This endpoint, since today, has to be accessible by the scanner to perform the analysis of the code.
I can confirm since yesterday our MSBuild started failing as they needed to reach a new endpoint…https://scanner.sonarcloud.io/ to download plugins. We had to add this endpoint to our outbound firewall rules to allow for additional external traffic. Scanning is working again. thanks.