Stefan Kangas <stefan@marxist.se> writes:

> So now Emacs 27.1 is released with harfbuzz support.  Could you please
> try this again using that and see if you can still reproduce this issue
> there?

I can still reproduce all of the above on both emacs-27 and master:

0. emacs -Q
1. C-x C-= C-= C-=
2. C-\ arabic RET
3. s ~ A

The kasrah is shown below the sin: