Non-manifold, bad contig Edges and Sharp Edges on simple basic geometry I have had issues trying to produce clean geometry for 3D printing for what is simple geometry. I check wether my mesh is clean or not using the 3D printing addon. Here is a step by step simple reproductible example starting with the defautl view to explain the non-manifold, bad contig Edges and Sharp Edges issues I have had and don’t understand : 

From the default start:


I change units from meter to milimeter 
I modify the view Clip start from 100mm to 0.1mm
I delete the default cube
I create a 10mm cube
I add a curve > Circle radius 3mm location X 0mm Y 0mm Z 20mm

I do a knife-project cut through

I select the two round faces in edit mode and press 2 to have all the
verticies of the two faces previously selected. 
I then bridge edge   loop them
I select all the verticies of the top circle and make a face (F key), notice below the 48 non manifold edge already because of that face:

Maybe it is because the top round face makes a zero volume if that object was to be printed right now? So I do an extrude 10mm on the three “top faces” to produce the final piece, I should then have a fully solid perfectly printable piece but below are three screenshots of the issues this mesh has:





What did I do wrong for those issues to appear on such basic geometry ?
I had a similair issue, although the shape had no inside-outside errors, still it was solved by  :    reset vectors-  recalculate outside

I'm guesing that while editing normals can get distorted, not alike the shape you see.