Qt Quick emulation layer crashed

Since I updated to 3.3.1 this afternoon, when I try to open mainForm.ui.qml file to edit, designer crashes with the message “Qt Quick emulation layer crashed (1:0)".

However, if I comment these lines:
property alias btOk: btOK
property alias btCancel: btCancel
property alias txtUtilizador: txtUtilizador
property alias txtPassword: txtPassword

that are the only declared properties, the message disappears, but all the previous layout it's gone.
If I run the application, it will run and work like before.