Steps to reproduce / test case:

Try the attached test application.

QScrollArea does not scroll to child widget that is outside viewport,
when tab focus moves from a sibling of QScrollArea to a child of
QScrollArea. (tab focus between child widgets scrolls ok).

A widget with many focusable child widgets is set as content for a
QScrollArea, vertical layout. Large enough, that many of the child
widgets are outside viewport. When moving focus with tab, initially
everything goes ok. When the focus loops back to the topmost child
widget, the QScrollArea does not scroll the widget visible. Only after
moving focus to the next child widget, the scroll area scrolls. Same
happens also when going backwards with Shift + tab.