We have today released Qt 5.6.1-1, which fixes a critical problem in Qt 5.6.1 preventing certain type of Qt Quick applications from working properly. I am very sorry for the inconvenience, but those who have already downloaded Qt 5.6.1 now need to get the new Qt 5.6.1-1 release. The problem is already fixed in the Qt 5.7.0 released last week.
The problem with Qt 5.6.1, reported in QTBUG-53761, is that certain Qt Quick applications crash after some time. The problem occurs with code that loads more than 64 components (.qml or .js files) without instantiating objects from all of them. The components that initially don't get instantiated will then be removed from the type cache, which causes problems if you later try to instantiate objects from them. Reason for the problem is too aggressive trimming of the QML type cache, which ends up deleting some QML types even though they were still in use by the application.
This bug was noticed and fixed just slightly too late for Qt 5.6.1 with https://codereview.qt-project.org/#/c/161888. It got into the 5.6 branch as well as into Qt 5.7.0 release last week. Furthermore, as the bug was a bit difficult one to diagnose, it was initially slightly misdiagnosed resulting it to be P1, not P0 as it should have been.
If you are using the online installer, Qt 5.6.1-1 can be updated using the maintenance tool. Offline packages are available for commercial users in the Qt Account portal and at the qt.io Download page for open-source users.