While working on a font-fallback issue, I created a table with a header which has all the characters required by AsciiDoctorPDF (☑ ☐) in the header row. However, the characters are rendered as missing glyphs.

This impacts both hard-coded and csv included files.
This appears to impact ONLY the default-theme; when I specify my own theme (using Windows fonts), the characters display correctly. To rule out any Windows issue, I re-created a minimal example on a Linux machine with a fresh install of AsciiDoctor-PDF and created it in Visual Studio Code.

asciidoctor-pdf version details:
Asciidoctor PDF 2.3.9 using Asciidoctor 2.0.20 [https://asciidoctor.org] Runtime Environment (ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [x86_64-linux-gnu]) (lc:UTF-8 fs:UTF-8 in:UTF-8 ex:UTF-8)

This bug was discussed on the zulipchat:
https://asciidoctor.zulipchat.com/#narrow/stream/288690-users.2Fasciidoctor-pdf/topic/Bug.20-.20Tables.20with.20Headers.20Render.20.E2.98.91.20or.20.E2.98.90.20as.20Missing.20Glyph

Minimal Example

= Testing Tables with Ballot Box Table Header
This minimal example shows a problem with some characters in the asciidoc header.
This was generated on a Windows and a Linux system from Visual Studio Code using the default theme/settings.

* [*] Ballot Box with Check
* [ ] Ballot Box without Check

.Table Hard-Coded AsciiDoc Table
[options="header",cols=3]
|===
|► \u25ba BLACK RIGHT-POINTING POINTER
|☑ \u2611 BALLOT BOX WITH CHECK
|☐ \u2610 BALLOT BOX

|► \u25ba BLACK RIGHT-POINTING POINTER
|☑ \u2611 BALLOT BOX WITH CHECK
|☐ \u2610 BALLOT BOX
|===

.Table Hard-Coded AsciiDoc Table
[%header,cols=3]
|===
|► \u25ba BLACK RIGHT-POINTING POINTER
|☑ \u2611 BALLOT BOX WITH CHECK
|☐ \u2610 BALLOT BOX

|► \u25ba BLACK RIGHT-POINTING POINTER
|☑ \u2611 BALLOT BOX WITH CHECK
|☐ \u2610 BALLOT BOX
|===