Unicode characters in neovim not showing unless font > 11

[Blacksuan19]

Describe the bug
few days ago Unicode characters like the pipe character in below recording stopped showing up inside vim for me without setting the font size to be larger than 11, the issue occurs inside and outside tmux so i don't think it's a tmux issue.

i have made no changes to my kitty, vim or tmux config neither have i updated neovim in a while so this is very sudden

To Reproduce
Steps to reproduce the behavior:

1. set kitty font size < 11
2. open a file with unicode characters such as ▏and ▌in vim
3. the unicode character does not show up
4. See error

Expected behavior
the character should be there no matter the font size or line height

Screenshots
https://i.imgur.com/P6dF2N4.mp4

Environment details
OS: Arch linux
Terminal Font: JetBrains Mono (other fonts such as FiraCode have the same issue

kitty 0.19.1 created by Kovid Goyal
Linux Dark-Castle 5.8.14-zen1-1-zen #1 ZEN SMP PREEMPT Thu, 08 Oct 2020 07:11:27 +0000 x86_64
                   '                      root@Dark-Castle
                  'o'                     ----------------
                 'ooo'                    OS: Artix Linux x86_64
                'ooxoo'                   Host: X550DP 1.0
               'ooxxxoo'                  Kernel: 5.8.14-zen1-1-zen
              'oookkxxoo'                 Uptime: 10 secs
             'oiioxkkxxoo'                Packages: 701 (pacman)
            ':;:iiiioxxxoo'               Shell: zsh 5.8
               `'.;::ioxxoo'              Resolution: 1366x768
          '-.      `':;jiooo'             Terminal: 2
         'oooio-..     `'i:io'            CPU: AMD A10-5750M APU (4) @ 2.500GHz
        'ooooxxxxoio:,.   `'-;'           GPU: AMD ATI Radeon HD 8670A/8670M/8690M / R5 M330 / M430 / Radeon 520 Mobile
       'ooooxxxxxkkxoooIi:-.  `'          GPU: AMD ATI Radeon HD 8650G
      'ooooxxxxxkkkkxoiiiiiji'            Memory: 105MiB / 7157MiB
     'ooooxxxxxkxxoiiii:'`     .i'
    'ooooxxxxxoi:::'`       .;ioxo'
   'ooooxooi::'`         .:iiixkxxo'
  'ooooi:'`                `'';ioxxo'
 'i:'`                          '':io'
'`                                   `'


LSB_VERSION=1.4
DISTRIB_ID=Artix
DISTRIB_RELEASE=rolling
DISTRIB_DESCRIPTION="Artix Linux"
Loaded config files: /home/blacksuan19/.config/kitty/kitty.conf
Running under: X11

Config options different from defaults:
adjust_line_height   2
background           Color(red=15, green=17, blue=26)
color0               Color(red=59, green=66, blue=82)
color1               Color(red=191, green=97, blue=106)
color10              Color(red=163, green=190, blue=140)
color11              Color(red=235, green=203, blue=139)
color12              Color(red=129, green=161, blue=193)
color13              Color(red=180, green=142, blue=173)
color14              Color(red=143, green=188, blue=187)
color15              Color(red=180, green=142, blue=173)
color2               Color(red=163, green=190, blue=140)
color3               Color(red=235, green=203, blue=139)
color4               Color(red=129, green=161, blue=193)
color5               Color(red=180, green=142, blue=173)
color6               Color(red=136, green=192, blue=208)
color7               Color(red=229, green=233, blue=240)
color8               Color(red=76, green=86, blue=106)
color9               Color(red=191, green=97, blue=106)
cursor               Color(red=255, green=65, blue=81)
font_family          JetBrains Mono
font_size            8.5
foreground           Color(red=216, green=222, blue=233)
url_color            Color(red=255, green=65, blue=81)
window_padding_width FloatEdges(left=2.0, top=2.0, right=2.0, bottom=1.0)

Additional context
issue occurs when kitty is run without any config with kitty --config NONE

[kovidgoyal]

Works fine for me in up-to-date arch linux with the following command

kitty --config NONE -o font_size=8 vim

Copy pasting the following shows
acters such as ▏in vi

the ▏character, which btw, is not a pipe character, but a unicode block
drawing character U+258f (left one eight block)

Are you sure this is happening inside vim only?

[Blacksuan19]

just checked it happens outside vim as well

font size 8.5

font size 11

happens when running with no configs as well kitty --config NONE -o font_size=8

font size 8

font size 11