I have been doing some experiments and although the export application works with G4P it does not work with your GEncoderKnob class which extends the GKnob class in G4P.
I believe that I understand what is happening but any potential solution requires source code changes in the G4P library code and therefore a new release.
I say ‘potential’ because I need to do some more testing. Also although I suspect the changes needed are very simple I will not be rushing out a new version because there are other issues waiting to be resolved for the next release.
I will keep you posted. 