paragraph is expecting to be gives some rich text, yet you are passing it plain text. Use rtfesc to fix special characters such as "-".

use RTF::Writer qw( rtfesc );

$some_text = 'Hello this-is-a-hyphenated-sentence';

$rtf->paragraph(
   \'\fs24',
   rtfesc($some_text)
);


$rtf->paragraph(
   \'\fs24\b',
   rtfesc("Anniversary-Date: $anniv_date"),
   \'\line'
);

# or

$rtf->paragraph(
   \'\fs24\b',
   rtfesc("Anniversary-Date: $anniv_date\n")   
);
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