Cannot access state in VaadinSession or UI without locking the session.

Vaadin 14:

  1. We went live with the Vaadin application. This is my first time going live. When we try to reload the whole page with the multiples tab (fill content from DB). This error comes only when load increases on the server like (10+ people). When one or two-person using the application no such error/exception comes.

Below is one of the code where this error comes:

private void reloadAssignmentButton_onClick(final ClickEvent<Button> event)
				+ "::AssignmentFileDashboardView:::reloadAssignmentButton_onClick:::::CAN_FILE_NUMBER"
				+ UI.getCurrent().getSession().getAttribute(ConfigProperties.CAN_FILE_NUMBER).toString());
		catch(final Exception e)
					+ "::AssignmentFileDashBoardView::assignmentRefreshButton_buttonClick::error:: " + e.getMessage()
					+ e.getStackTrace(), e);

This is my tomcat configuration:

<Connector port="8080" protocol="HTTP/1.1" connectionTimeout="30000" redirectPort="8443" maxThreads="1000" minSpareThreads="50" acceptCount="300" enableLookUps="false" maxKeepAliveRequest = "1"/>

  1. Clicking these tabs some time stops working. Again with one or two users, it works fine but sometimes stops working.
  2. Sometimes I click on the tab and page load blank. again no problem when 1 or 2 users use it.

(Initially, I thought the tab might be having an issue and I change the tab to multiple buttons thinking the button will always call click event no matter what but now button also sometimes doing the same thing.)

We are live please help me. Thanks in advance.