If you are experiencing any issues with cell links returning blank entries (when there is data present in the source file) the current resolution is to manually remove the link, save the sheet and then put the link back.
Whilst this activity needs to be logged to Smartsheet Support and their experts are working on a resolution, we have an interim tool that can help identify the "blank cells" and relink them for you.
Reach out to me if you'd like more information.
Kind regards
debbie.sawyer@smarterbusinessprocesses.com