Google Sheets has a maximum limit of 2 million cells to be used inside a single spreadsheet document. If you are close to this limit, then the spreadsheet performance will decrease and Import Sheet might encounter problems exporting or import data in reference to this document. To decrease the number of used spreadsheet cells:
- Remove any blank and unused columns,
- Remove data that is no longer being used,
- Split data into separate spreadsheets, create summaries inside these and consolidate the summaries back into a single master spreadsheet.