When the vaadin app is non-responsive like this, what is the best approach to be followed?
The blue bar on the top appears when the processing of a HTTP request takes long. If you are seeing the same in your own application, the reason might not be the same. I would assume that in case of that demo app, the most likely cause is that it is run on minimal server resources and therefore might not be able to serve all users when there is high traffic. There can be many other reasons why HTTP request takes long. For example if you have synchronous backend access and your database is slow.