the current LibreCAD hatching feature requires a simple and closed contour:
1, simple, it means not self-intersecting;
2, closed means each end point of entities within the contour must be the start point of one and exact one entity of the contour;
microm wrote
In you file all squares have points in line intersection.
In my file squares drawn with long lines without points in intersections.
Draw with lines symbol "#" and try to fill them inside lines.
p.s.
Original file was created in DWG with proprietary CAD and exported to dxf format.
Later dxf opened in same CAD and looks normal.
Also look normal in qcad.
But in librecad its not look normal.
Trying to open dwg was produced librecad crash.