I think I have figured out the second part; Dash tries to invoke setProps, but that property doesn’t exist on the customly rendered component. Assigning an empty function to setProps solves this issue. This fix has been implemented in dash-extensions-js@0.0.6.
I still haven’t figured out how to address the warning. However, I have noticed that it appears only in debug mode. When debug is set to false, I don’t see any errors (or warnings). Do you know what is wrong, @chriddyp? 