"Vaadin Bakery App Starter for Flow and Spring" Concurrent Users Issue

I have taken starter application from https://vaadin.com/start/v10-full-stack-spring. There are two users i.e. admin@vaadin.com & barista@vaadin.com.From one system I opened 10 chrome browser instances concurrently with user “admin@vaadin.com” using Vaadin TestBench. Parallelly, from another system I tried to logged in with 3 different browsers(i.e. Chrome,Opera,Mozilla) with user “barista@vaadin.com” without TestBench.
The issue is:

  1. It can handle all 10 requests in first system(using TestBench) and navigated to Storefront page successfully.
  2. But in 2nd system, though I clicked on Sign In Button, it is not navigating to Storefront page and it is redirected to login page itself.(Sometimes it will not load Storefront in all 3 browsers, sometimes it will load Storefront in 2 browsers and skip 1 browser, meaning it is not fixed in how many browsers it will load storefront page).
    Can anyone help on this? Thank you !!!