Debugger - Variables not accessible

Some variables cannot be read in the debugger. In my case those variables have Qt types but for what I've read in forums, it applies also to other types, like those in the STL. For such variables Qt Creator displays the value <not accessible>. This happens in the locals section and in the watch section of the IDE.

Apparently, this problem has occurred in different versions of Qt Creator (3.0, 3.1.2, 4.5.1, 6.2.0, 14.0.1) and doesn't have a solution in forums:

• https://stackoverflow.com/questions/21254074/how-to-solve-qt-creators-variable-not-accessible-behavior
• https://forum.qt.io/topic/121061/debugging-vars-not-accessible
• https://forum.qt.io/topic/142415/qt-creator-debugging-variables-not-accessible
• https://stackoverflow.com/questions/20610186/variables-in-locals-and-expressions-not-accessible-in-qt-creator
• https://forum.qt.io/topic/132899/unable-to-debug-variables-not-accessible-or-with-wrong-values

This doesn't occur in other IDEs like CLion or VS Code. Please refer to the images. Just as a reference, I used the following code for debugging

void ThumbnailView::keyPressEvent(QKeyEvent *event)
{
    if (event->key() == Qt::Key_Return) {
        ...

    } else if (event->key() == Qt::Key_Right && event->modifiers() == Qt::NoModifier) {
           ...

        }
        return;
    }

        QListView::keyPressEvent(event);
}

Qt Creator

CLion