Link to Gnome bug:
Patch tested in gnome. Patch to follow.
The underlying problem is that the old code invoked by cli_write() increments cli->mid directly when issuing outstanding writes. This should now be done only in libsmb/clientgen.c to make metze's new signing engine work correctly. Just deleting this code fixes the problem.
I'm working on adding a smbtorture test for this before checking in the patch.
Created attachment 6062 [details]
git-am fix for 3.5.7.
Original Gnome submitter reports this fixes the bug.
Raised priority to critical as this breaks Gnome desktop copying to all signed servers.
Pushed to v3-5-test.
Closing out bug report.