FreeRTOS: Program freezes when manipulating Qul::Property<std::string> or std::stack<std::string>

// customstackviewbackend.h
struct CustomStackViewBackend : public Qul::Singleton<CustomStackViewBackend>
{
    CustomStackViewBackend() {}

    void push(std::string view)
    {
        _view = view; // Works fine
        // stackViews.push(view); // Freezes the program
        // lastView.setValue(view); // Freezes the program;
    }

    Qul::Property<std::string> lastView;
    std::stack<std::string> stackViews;
    std::string _view;
};

// CustomStackView.qml
pragma Singleton
import QtQuick

QtObject {
    signal screenUpdate(string screen)

    function push(url: string) {
        CustomStackViewBackend.push(url)
        screenUpdate(CustomStackViewBackend.lastView)
    }
}