OK, I got it.
The thing is that I use PUREMVC Mediator and Notification. On the first load, everything's good as the async method that returns data for DynamicForm C is sending the successful notification AFTER I have already created the VLayout B, and thus the addMember method adds and displays the DynamicForm C.
On the second load, I use the data that has already been gathered from DB, so no async method is being processed and the notification arrives BEFORE I create VLayout B, so basically the DynamicForm C is NOT being drawn.
My solution : I reordered some lines of code to make sure I always call the method that sends data via Notification (whether from DB or stocked) AFTER of the page creation.