I use RealDWG to create a new DWG file, then create a new block called "MyBlock", then add some lines, to "MyBlock", then when I open the DWG file in AutoCAD, I cannot find the lines at all. However, if I click "Block Editor", then I will see a list of the blocks including "MyBlock", and when clicking "MyBlock", I will see a preview of the block which contains some lines. But I still cannot see the lines when in the main window.
It sounds like you are creating a block definition, but there is no actual insert of that block in the drawing.
I think you simply need to insert a copy of the block (definition) into the DWG that contains the block definition.