While performing an operation, the ShareGate migration tool displays the following message:
SharePoint is not responding to connection requests from the ShareGate migration tool at this time. The app will attempt to reestablish the connection in 1 minute.
Any error ending with -289
This message is displayed when the ShareGate migration tool receives too many network errors while trying to send requests to SharePoint or Microsoft 365. This could happen if your local network or the servers are too busy or down.
The result is that the ShareGate migration tool pauses the operation for a moment and then retries at a later time. It will start by waiting 1 minute and, if it keeps failing, it will gradually increase the wait time to a maximum of 1 hour (it will retry every hour until it succeeds or until you cancel the operation).
At any moment, you can force it to retry now by clicking on Retry.
If the problem is that the server or the network cannot handle the number of requests being sent by the ShareGate migration tool, it can help to lower the performance level. This will lower the number of requests the ShareGate migration tool can send simultaneously, which can help your network and/or server handle them.
If the issue persists reach out to your network or SharePoint administrator to see if something prevents the ShareGate migration tool from operating properly on your network or server.
Tip: The article Which ports does the ShareGate migration tool require to be open in our proxy or firewall? and the Advanced section of the Troubleshoot SharePoint on-premises connection issues article are good references for a network or SharePoint admin to investigate the cause of these problems.