UIC generated header file does not recognize path to include custom widget header

Question

I made a custom widget plugins library for Qt 5 and it was working fine till I upgraded my OS (to ubuntu 19.04).

In current version (5.12) UIC can not generate the ui_ header file... Makefile declares custom widget header as a dependency for the cpp file using it:

ui_dialog-rectangulation.h: ../anr-0.1.5/src/gui/dialog-rectangulation.ui \
        /usr/lib/qt5/bin/uic \
        qtz/widgets/viewers/image-viewer.hpp
    /usr/lib/qt5/bin/uic ../anr-0.1.5/src/gui/dialog-rectangulation.ui -o ui_dialog-rectangulation.h

Though the dependency can not be met:

make: *** No rule to make target 'qtz/widgets/viewers/image-viewer.hpp', needed by 'ui_dialog-rectangulation.h'. Stop.

and the ui_... is not generated.

The widget plugin library declares include file like this:

QString ImageViewerPlugin::includeFile() const {
    return QLatin1String("qtz/widgets/viewers/image-viewer.hpp");
}

The path is correct, header file exists there, though Makefile does not include full path to such file (see above).

Questions:

• Should Makefile it include full path? in that case what should I return from ImageViewerPlugin::includeFile()?
• In general what am I doing wrong with these widgets? It used to work fine with Qt 5.9 on Ubuntu and Windows. Source code is available at https://github.com/soroush/qtz-widgets, and the plugins library is available at https://github.com/soroush/qtz-plugin