I see that you have an issue with your On-Premise Gateway that is being used to save server modifications. The Gateway on the specified endpoint ('sb//wabi-north-europe-relay7.servicebus.windows.net') is reported as unreachable.
Try to verify the status of the On-Premise Gateway configured for your environment. Ensure that the Gateway service is running and there are no reported issues or outages. If necessary, restart the Gateway service and monitor its status.
Ensure proper network connectivity between the server where the cube processing is initiated and the On-Premise Gateway endpoint. Check for any network issues that may block communication, such as firewalls or proxies. You may need to involve your network administrator to assist with network troubleshooting.
You can double-check the configuration settings for the On-Premise Gateway. Ensure that the Gateway is appropriatelyy registered and associated with the correct endpoints. Verify the authentication settings, credentials, and any required certificates.
If it is possibl,e share with us the logs and event viewer on the server where the Gateway is installed for any relevant error messages or indications of issues. The logs might provide additional details on the cause of the Gateway being unreachable.
I remember that once the Gateway was outdated so I had to update it to the latest version.