@iignatov Thanks anyway. 
I just spent a few hours more trying to resolve this with no success, argh! If I change the ‘watch’ in the following gulp task (in gulpfile.js) to ‘build’
gulp.task('serve:before', ['watch']);
thus bypassing all the watching (and those errors) I still get an app.bundle.js with the same content as my first post (i.e. without the actual app.ts/js code included). The app.bundle.js.map file does include the app.ts/js code though, so that’s confusing.
So it may be related to the code in the gulp tasks
var buildBrowserify = require('ionic-gulp-browserify-typescript');
var copyScripts = require('ionic-gulp-scripts-copy');
which I believe are responsible for creating app.bundle.js.
But that’s enough for me for today, will have a look at these tasks further if I still have the enthusiasm in the next few days…