When exporting images that have their background hidden, the grid is rendered in them if it's displayed in the application.
To reproduce the issue with the example file, display the grid, select the gray image background using the Arrow tool, hide it by pressing F12, and then perform File -> Export -> Pages.
Example file: https://www.dropbox.com/s/fi47peyxxvhqf … d.pdf?dl=0
Thank you for reporting the issue with Infix.
This issue has been fixed and the fix will be included in the next point release of Infix (7.2.5).