I have horizontal lines in my Google Doc but they are missing when I create a PDF with the Grackle Docs Add-on.
We have seen this behaviour and have logged a ticket with Google.
We work with Google APIs and the line drawn by using the “Insert->Horizontal Line” does not get passed through to the Add-on correctly. The best solution is to utilize tabs and then apply a border to it. Underscores may cause problems for screen readers where tabs will be ignored. Create a line of tabs and then select the entire line of tabs and utilize the Format->Paragraph Styles->Borders and Shading Option and apply a border under the tabs.