I lied. I ended up investigating it further 
To fix it, edit /etc/hestiacp/hooks/pluginable.php and add this line:
$html = html_entity_decode($html, ENT_QUOTES | ENT_HTML5, 'UTF-8');
Before this line:
$dom->loadHTML( $html );
If you don’t want to edit it manually, execute this sed command:
sed -i.bak 's/\$dom->loadHTML( \$html );/\$html = html_entity_decode(\$html, ENT_QUOTES | ENT_HTML5, '"'"'UTF-8'"'"');\n\t\t\$dom->loadHTML( \$html );/' /etc/hestiacp/hooks/pluginable.php
Remember to restore the change you did in function tohtml in /usr/local/hestia/web/inc/helpers.php.