QJSValue misbehaves on android, I can't explain it.
The following code:

QJSValue jsv = mEngine->newObject();
jsv.setProperty("name", "John");
auto temp = jsv.property("name").toString();
qDebug() << temp;

prints: "1.0985603458179353e+58"

If I create a simple "hello world" project with the same kit and run it on the same phone, it prints "John" as you would expect.