Welcome to the forum.
Exports from Monarch to that Excel file will fail if the range name has been corrupted. Open the Excel file and examine the list of range names, and specifically the ranges to which those names apply. If you see #NA or some other error in the range that Monarch is using for exporting, then you need to delete that range name, or manually make it a valid, legal range before Monarch will export properly to that file.
My recommendation is to keep all Monarch exports on their own worksheets, and then build formulas on other sheets to refer to those Monarch data tables as necessary for your other Excel analysis work. Leave the Monarch stuff alone and all will be well. Modifying it in any way, like deleting the first or last row or column, and the named range will "blow up" and Monarch won't be able to export to that file (with that range name).