The magic number in GZip header is not correct error

You've robocopied your latest WSUS updates to your offline WSUS server, but upon trying to use WsusUtil.exe to import the metadata, the above Fatal error occurs.

There are already some articles out including on Serverfault website:

https://serverfault.com/questions/714169/wsus-export-error-the-gzip-stream-cannot-contain-more-than-4gb-data

And others which go into lengthy process such as resetting WSUS and deleting WID database....

But try this simpler step first:

In your WSUSContent folder delete the export.xml.gz and then rerun the original RoboCopy process.

Once complete, rerun the WSUSUtil import of the metadata. It should complete successfully.

It's easier to try this before the heavier tactics posted elsewhere.