This is a workaround solution to the problem of Shopify line item properties getting truncated and stripped of their line breaks on the Orders page. I convert line item properties to unique cart attributes to move the information to the Order Notes section of the Orders page.

Shopify Line Item Properties -> Cart Attributes

{{ p.first }}{% endunless %}: {{ p.last | newline_to_br }}
<textarea class="hidden" id="{{ p.first | handle }}-{{ item.product.handle }}" name="attributes[{{ p.first | handle }}-{{ item.product.handle }}]" cols="10" rows="10">{{ p.last }}</textarea>