Unable to drag scrollbar in scroll area in Qt 5.6.3 widgets application

[Ramakanth]

UI Application is Qt 5.6.3 widgets based on 4.14 linux kernel built with yocto meta-qt5 recipes.

For all different views like QTableView,QTreeView, am using the inbuilt QScrollBar.

The mouse wheel works, the up and down arrows on the bar work, but unable to drag the scroll bar using the mouse.

For example, below are set for custom QTableView:
setVerticalScrollBarPolicy( Qt::ScrollBarAlwaysOn );
setVerticalScrollMode( ScrollPerItem );
setAcceptDrops(false);
setDragEnabled(false);
setAutoScroll(false);

Do we need to enable any macro to make drag work or do you see any issue on the above which makes drag the scrollbar doesnot works in Qt 5.6.3?
Appreciate for the suggestions in this regard.