Not sure if this was ever solved, but if you remove the app from $SPLUNK_HOME/etc/app/your_app and under any user directories, and remove $SPLUNK_HOME/etc/app/splunk_app_addon-builder, then reinstall the splunk app add-on builder and restart splunk, you should be able to re-import your app no problem. I'm not sure what remnants get left behind in one of the app add-on builder files, but this worked for me.
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