I have the same problem: I have converted and imported a different font (Arial). The letters display and print as an unfilled outline. Is it possible to use hatch - or some other tool - to make the letters solid?
Basically you can hatch unfilled outline text if you "Explode" it first. Of course you can't edit it as text anymore afterwards and the result depends on the used font. It more often works badly ( some letters don't respond at all, at others you get artifacts) than it works well. You have to try it out.
Also see here: https://github.com/LibreCAD/LibreCAD/issues/1558