A common cause of this is thought to be where, due to an update the columns included in the 'gridview' which is an individual user preference have either been removed from the core code search update or have been renamed/or reordered in the core code.
As a result the optional user preference of saving the grid view in Configure Columns no longer works and so has to be reset. To do this:
On the Enquiry window click the CogWheel and select Configure Columns
Click Reset.
Click OK. This will reset the user preferred columns, including the selected and ordering of columns to the standard columns.
Reconfigure the columns to your preference again.
Export to Excel as usual.