There might by a style property applied to your grid to prevent page breaks in the element.
Have a look if you find something like 'page-break-inside: avoid' on your grid or table in the properties pane.
Or perhaps an 'overflow: hidden' on the grid or table which prevents the rest of the rows from rendering.
Here's a similar question, though it doesn't have an accepted answer - maybe it'll help: https://forum.mendix.com/link/space/studio-pro/questions/86292
Otherwise, if you have the option, I would highly recommend the new PDF Document Generator, which makes this sort of thing a lot easier.