Can’t generate PDF on some posts – PHP error shown

Have just installed this on a blank installation of 4.9.8 with just this installed and trialled, but am getting the error below on any meaningful content.

Does work:

Text: Works
Text + Images: Works

Text + Images + Links + Styles (bold): Works

Introducing list elements: Opens Chrome PDF viewer with error “Failed to load PDF document”

When I tried to create a complex page, or alternatively to isolate it I copy and pasted your demo post: https://bestwebsoft.com/live-buttons-preview/ I get the error below

Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 30649 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 30649 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2006 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2006 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2006 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2006 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2006 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2006 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 1889 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2006 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2006 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php on line 2003 Warning: A non-numeric value encountered in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 6387 Warning: Cannot modify header information - headers already sent by (output started at /app/public/wp-content/plugins/pdf-print/mpdf/Tag.php:2003) in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 9403 Fatal error: Uncaught MpdfException: Some data has already been output to browser, can't send PDF file in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php:9405 Stack trace: #0 /app/public/wp-content/plugins/pdf-print/pdf-print.php(1037): mPDF->Output() #1 /app/public/wp-includes/class-wp-hook.php(286): pdfprnt_print(Object(WP)) #2 /app/public/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters('', Array) #3 /app/public/wp-includes/plugin.php(515): WP_Hook->do_action(Array) #4 /app/public/wp-includes/class-wp.php(726): do_action_ref_array('wp', Array) #5 /app/public/wp-includes/functions.php(960): WP->main('') #6 /app/public/wp-blog-header.php(16): wp() #7 /app/public/index.php(17): require('/app/public/wp-...') #8 {main} thrown in /app/public/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 9405