I build app successfully when I run app on real android device, White Screen is open for 5s then this app will crash and show this msg the connection to the server was unsuccessful. (file ///android_asset/www/index.html)
sorry for the delay in answering, it's been some crazy months lately.
This error is displayed because the app takes too long to load. You can increase the accepted load time by adding this line to config.xml (it was already added to the v3.5.0 branch of the app):
<preference name="LoadUrlTimeoutValue" value="60000" />
When building for release you should compile using AOT mode so it loads faster, I'll add instructions on how to do it in the development guide.