Face where there should be no face
At the intersection of the top and bottom planes of the cross-piece and the cylinder, there are non-manifold edges. Meshmixer is able to identify this problem but cannot repair it. My slicer, Simplify3D also identifies the faults and prints a solid cylinder between the planes. Prusa Slicer 2 also creates a solid at that location.

As you've indicated that you are the creator, consider to use the 3D printing features within Blender to assist you with repairing the problem locations.


  File ‣ User Preferences (or Ctrl-Alt-U)
  to open the User Preferences menu.
  
  In the Add-ons tab, start typing 3d print into the search bar. Once
  the “Mesh: 3D Print Toolbox” shows up, click the checkbox on the far
  right to enable this add-on.
  
  Close the User Preferences window.
  
  In the Tool Shelf, there should be a new 3D Printing tab.