In 5.12.1, the symbol "column" (all lower case) seems to be an undocumented symbol which causes mis-behavior if user QML code declares a Column object using id: column.  This problem appeared some time since 5.8.

Internal identifiers should use some naming convention to prevent clashing or interfering with user code, for example using an initial underscore.

In this case, the published example for using callLater() in https://doc.qt.io/qt-5/qml-qtqml-qt.htmlis broken because of this (the example is supposed to change the width of all displayed items to be the width of the widest item, but doesn't; if the id "column" is changed to something else then the example works).