Figured it out!
there was one line of suspicious code in that class at the very top
internal ESRI.ArcGIS.ArcMap.Application esriArcMapApplication_definst = new ESRI.ArcGIS.ArcMap.Application();
not in the constructor just right in the top of the class with the other class vars
so I did a Find all refs on that var
with zero hits
so I commented that line out
now it shows up just fine in catalog!
Always check to see if there's anything strange in the class vars area of your AUs if you run into this same issue.
Was that code in the original vb6 version, or did it get converted to some other language? Typically in .net applications we recommend not direclty instantiating the application or application class. Instead make use of the app ref singleton or the hook helper.
I don't see that line of code or even anything similar in the original VB6 code so it must have come over when upgrading to C#. Which makes sense because that variable wasn't used anywhere else. I will have to ask how it was upgraded or if an upgrade tool or visual studio was used to do the conversion to see how that got in there.