All, very annoying and thorny problem.
Solution A - I have defined a new DAML category
<insertCategory id="my_special_tool"/>
This solution has an ArcGIS Dockpane which loads in Embeddable Controls using the ContentPresenter pattern. This works quite well.
Solution B - Has 2 projects which contain the embeddable controls (defined as ArcGIS Modules, with Embeddable controls added)
In the categories section in their DAML's I have
<categories>
<updateCategory refID="my_special_tool">
<insertComponent id="Control1" className="Control1ViewModel">
<content className="Control1View" displayName="Control1" />
</insertComponent>
</updateCategory>
</categories>
and the second is
<categories>
<updateCategory refID="my_special_tool">
<insertComponent id="Control2" className="Control2ViewModel">
<content className="Control2View" displayName="Control2" />
</insertComponent>
</updateCategory>
</categories>
I can build both modules and see them get added as addins to the Pro system. When I start Pro and load my dockpane I can issue the call
var cat = Categories.GetComponentElements("my_special_tool")
I used to get both addins (Controls), then suddenly my second addin just stopped working. No matter what I try, deleting the addin cache, rebooting, nothing will enable the second one to be seen. It is almost like Pro, on startup isn't reading the second addin's DAML file (though I can see it's installed). Using the GetComponentCategories, it returns only the 1st solution and not the second.
Any thoughts / options / troubleshooting tips would be much appreciated. I have had this before and I just created a new solution, but surely there must be a better way of dealing with components that just stop loading in Pro.
Thank you