Posting this in case it helps someone else.
When using SSL exporting reports to pdf would cause a long timeout followed by an error.
Enabling debug in the report via:
select 'dbr.export.options', 'debug', 1;
Gave the command line to exec. That showed the following errors:
wkhtmltopdf -q --header-html https://host.domain.com/mydbr/user/export_header_pdf.php --margin-top 20 --header-spacing 8 /tmp/126088698.html -
QSslSocket: cannot call unresolved function SSLv3_client_method
QSslSocket: cannot call unresolved function SSL_CTX_new
QSslSocket: cannot call unresolved function ERR_get_error
QSslSocket: cannot call unresolved function ERR_error_string
The solution is to
yum install openssl-devel
Then all works as expected.