Office 365 Workflow Not Starting Automatically

Try to include a pause of some duration or add a filter condition on the ListB to run the workflow only when ID is not null

This is as expected.

Workflows start on user actions not system actions. Nintex creating a list item in another list is a system action and therefore doesn't fire off the workflow on that list.

Simple to implement a "Start Workflow" action after the create list item action, have the create item stored to ID it just created as a variable and use that in the Start Workflow action as the item ID.

On the onpremise version.I am able to trigger the workflow on both the lists but I am not using system account."Create Item" action triggered workflows on both the lists

Yes on-premise there is a farm setting you can configure to start workflows on system actions.