Cut & paste also worked for me (needs to be the Artboard, not a child element of the artboard, right click on artboard in layer list, Cut, then again and Paste Here)
Re-rendering breaks it again
Duplicating the Artboard makes the duplicate show up in the mirror
If a new document is created it will be shared with mirror as layers are added in Sketch, but re-rendering RSA into the document yields the "This Artboard cannot be retrieved" for each Artboard.
In Sketch, if Mirror > {local url} is clicked, the browser does show the RSA rendered artboards without any of the about workarounds necessary.
Reporting a bug or issue
React Created Artboard could not be retrieved by the mirror app.
How to reproduce:
Use Artbord to create an artbord.
or try react-sketchapp/examples/foursquare-maps
Connect Mirror to your Sketchapp.
BUT Cut and past the artbord fix the issue.
Sketch version: 48.2
react-sketchapp version: 1.0.0
React: 16.2.0