I really appreciate your effort.  I have tried to modify existing hatch files, without circles, polylines etc. No success. I have also gone through the other efforts you list. This is enough of a problem for me to abandon LibreCAD. Too kludgy for prime time. Thanks again.

From: dellus [via LibreCAD] <[hidden email]>
Sent: Thursday, December 12, 2019 6:32 AM
To: figurado <[hidden email]>
Subject: RE: Hatch patterns available?

That is a hard nut - I couldn't crack it.
First I found and deleted a very tiny copy of the content of the 100x100 box somewhere left and below the origin. Then in the Block List I discovered and deleted unused blocks. I moved the drawing's content to Layer 0 and deleted the others. Set units to None and paper size to A4 (standard). I got the file size down to 104 kB.
But to no avail. Further experiments showed LC hatches don't accept circles, splines and polylines. Seems there is a lot to investigate.