I use QGIS 2.18.0 on Windows 10.
I wanted to add a layer from PostGIS using the DB Manager. After choosing the "unique column" and the "geometry column" the DB Manager did not load the layer. However, without any error message or hint. The reason why it did not load was that there were columns with the same name (duplicate column names).
Does DB Manager usually tell me about duplicate column names?
(or is this "feature" not implemented?) (or is my QGIS version too old?)