Myanmar Unicode fonts do not render correctly. This is due to
QTBUG-5472 and also the following reason:
Qt uses the old Harfbuzz Unicode 4 Myanmar shaper which does not work with Myanmar Unicode 5.1 fonts - most Myanmar Unicode fonts use just the default OT features since that is all that Uniscribe supports.
Please can Qt switch to Harfbuzz-NG or consider the patches at https://bugs.freedesktop.org/show_bug.cgi?id=31003