May be it is issue from your system ? Or Since you are calling qml methods directly from C++, something may be hung or got into deadlock ? There is no specific order of call. It is just method call. If it is multithread application & it may be work slightly differently.
Best approach is write a small QML application. Use timer to continuously update the qml with some random text. Observe for the period you said. This may give you the hint on where the issue exist.