AudioPluginHost doesn't show AUv3 from saved filtergraph

I have a question about the AudioPluginHost app (on a Mac) and AUv3 plugins. The AudioPluginHost won’t load/display AUv3 plugins when opening a saved filtergraph file. I am able to to add an AUv3 plugin and use it in AudioPluginHost. I save the filtergraph file and I can view that file (with a text editor) and see that the information for that plugin is in the file. But if I open that file with AudioPluginHost, the plugin is not visible. I tried both a VST3 and an AU and both of those work. I can save the file and reopen it and they show up within the work area of the host.

I also built an AUv3 plugin with Xcode “natively” (no JUCE involved) and it has the same behavior as the one built with JUCE (it does not show up when loading a saved filtergraph file).

Note that both the AUv3 and the AU plugin I built seem to work fine with Logic Pro X. So I think I am building them correctly.

Is this expected to work? I am mostly just trying to understand how everything fits together.