Here are the steps to reproduce:
1. emacs -Q

2. enter these three words:
hṛṣyatha (h#x1E5B#x1E63yatha)
kṣiptaḥ (k#x1E63ipta#x1E25)
viśāmaḥ (vi#x015B#x0101ma#x1E25)

At this stage everything is fine, all of the characters use the same font
therefore all of them return the same font after evaluating (font-at
(point)) on them:
#<font-object "-ADBO-Source Code
Pro-regular-normal-normal-*-32-*-*-*-m-0-iso10646-1">

3. Now eval the following in the buffer
(set-face-attribute 'default nil
   :font "JetBrains Mono"
   :weight 'regular
   :height 170)

Now you'll notice that the font for some of the characters above are
different from JetBrainsMono, these characters are:
ṛ (#x1e5b)
ṣ (#x1e63)
ḥ (#x1e25)
(font-at (point)) returns #<font-object "-UKWN-Latin Modern
Mono-regular-normal-normal-*-57-*-*-*-*-0-iso10646-1"> on all of them
while for the rest of the characters gives #<font-object "-JB-JetBrains
Mono-regular-normal-normal-*-57-*-*-*-m-0-iso10646-1">

Changing the weight from regular to medium also does not help, the
offending characters instead of being displayed with Latin Modern Mono are
now displayed with: #<font-object "-GOOG-Noto Serif
Display-medium-normal-normal-*-57-*-*-*-*-0-iso10646-1">
while the rest of the characters are displayed with #<font-object
"-JB-JetBrains Mono-medium-normal-normal-*-57-*-*-*-m-0-iso10646-1">

I have also included screenshots from emacs -Q before, emacs -Q after and
hb-view from JetBrains

Hope this makes things clear, if something is still missing please tell me.
Thanks


On Fri, Sep 30, 2022 at 11:33 AM Eli Zaretskii <eliz@gnu.org> wrote:

> > From: समीर सिंह Sameer Singh
> >  <lumarzeli30@gmail.com>
> > Date: Fri, 30 Sep 2022 04:49:37 +0530
> >
> > codepoints of faulty characters in the above mail:
> > ṣ #x1e63
> > ṇ #x1e47
> > ḍ #x1e0d
>
> Please _always_ show the actual text, not just an image of its
> display.  It is practically impossible to know what text you used
> given just its display screenshot, especially when character
> compositions are involved.
>
> In any case, we will need a reproducible recipe starting from
> "emacs -Q".  Also, please include in your report the output of
>
>    M-: (font-at (point)) RET
>
> for the "good" and the "faulty" characters.
>
> In general, reporting issues with fonts need as many specific details
> as you can collect, because these issues are inherently
> system-specific, due to different sets of fonts installed on each
> system, and due to font customizations that are outside of Emacs (on
> the Fontconfig level).  The probability of getting unreproducible
> results is very high, and each detail helps.
>