Undefined offset: 1 - by: xSmorpheusSx

2017-12-27 11:00:18.883 ***** ERROR ***** [V6.4.4] ERROR *****
2017-12-27 11:00:18.886 ***** ERROR ***** [V6.4.4] on file 'D:\xampp\htdocs\projeqtor\external\html2pdf\html2pdf.class.php' at line (2197)
2017-12-27 11:00:18.888 ***** ERROR ***** [V6.4.4] cause = Undefined offset: 1

Steps to reproduce:

1. Follow-up
2. Reports
3. miscellaneous
4. project dashboard
5. export to pdf format

PHP Version: 7.1.12

Thanks for helping