When operating, ShareGate Migrate displays the following error:

The SharePoint server returned an error: "(502) Bad Gateway". This normally happens when there is a communication failure between 2 servers.

This error occurs when there is a communication failure between 2 servers while SharePoint tries to process the request sent by ShareGate Migrate. The 2 servers are most likely 2 servers of the SharePoint farm, but it can also happen when a proxy is involved in the connection, and an error occurs between the proxy server and the SharePoint server. The problem behind the error is generally a problem with the network, which can be a temporary failure or a permanent configuration issue.

The first thing to try is to retry the same operation later since a temporary network failure could cause the issue. If the problem persists, you should contact your network administrator to let them know that you are getting Bad Gateway errors from the SharePoint server. It is also worth looking into the SharePoint ULS logs and the IIS logs to see if there is anything indicating the source of the error.