Weird application crash

[wysota]

You can't make an incorrect code work. Finding the real problem with a bad design will take more time than rewriting it using correct solutions. Either implement the model by subclassing from QAbstractListModel or switch to QStandardItemModel completely.

[MarkoSan]

I've switched to QStandardItemModel, you saw it in the header file!!

And the order list simply cannot be redundant because I need it in other parts of project. So I cannot have QStandardModel with this list or what now?!

[wysota]

I've switched to QStandardItemModel, you saw it in the header file!!

No, you didn't. You subclassed the model (and did it incorrectly) and not used it.

And the order list simply cannot be redundant because I need it in other parts of project. So I cannot have QStandardModel with this list or what now?!

I don't know what can or can't be. I know all the functionality of your list is already in the standard item model. So either don't use the list or don't use QStandardItemModel. A proper approach is to get rid of QStandardItemModel, but it's more work to implement your own model instead of using the standard one.