I have a similar problem with callouts in PDF. The font I have configured do not support special chars like
circled digit one.
You are probabelly experimenting something similar with
rightwards double arrow.
Are you seing something like that in your log:
"The following text could not be fully converted to the Windows-1252 character set" ?
See:
https://github.com/asciidoctor/asciidoctor-pdf/issues/409