but that did not solve the issue.

However, I have been using the xft+harfbuzz combo for a ~week now and I
can say with confidence that I don't experience this strange issue.  I
would highly appreciate it if the decision to remove the xft backend
could be delayed until a solution comes up [1].  Although the font
rendering is worse, the text stays readable at all font sizes.


[1] ./configure --with-cairo says,

    configure: WARNING: This configuration uses libXft, which has a number of
        font rendering issues, and is being considered for removal in the
        next release of Emacs.  Please consider using Cairo graphics +
        HarfBuzz text shaping instead (they are auto-detected if the
        relevant development headers are installed).