Safari gets network connection reset over https with very high speed connection

[jb]

Does anyone know how I can debug this issue?

nginx (latest version and 1.9 too) running on iMac
Safari running on macbook
thunderbolt2 cable between the two of them.

Any download of https file from nginx downloads random start part of the
file then
Safari reports in red "The network connection was lost".

No other browser has an issue.
Doesn't happen with http only https
doesn't happen if the connection is throttled down to less than 400 megabit.
Happens faster, the faster the connection is...

Nothing in the nginx error log.

I've reported the bug to Safari however from their response I believe they
are not going to find the issue.

Can anyone with a fast https connection - maybe to localhost - confirm this
problem? Under Sierra and Safari 10. I don't know if the older version of
Safari also had this.

thanks
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