DWG support is still rudimentary in LibreCAD.
Maybe it contains yet unsupported entities or it's a bug related with libdxfrw, LibreCAD's import library.
If you can share the file, you can post it here, then we can do further investigations on it.
Otherwise you can look for a DWG to DXF converter and use the DXF file with LibreCAD.
investing less than half an hour into Search function can save hours or days of waiting for a solution