QML interface not fully initialised when main window is shown

This isn’t enough information to go on. Can you create a small code sample that replicates the problem? In the meantime I’ll take a stab in the dark. Having a long running process in the main GUI thread can cause problems. The UI won’t properly display until the event handler is running. If you have some initialization task that takes a while then you need to use a worker thread to handle that and let your GUI thread complete.