When you open an exported CSV in Excel, there are a few fields that may not initially display your data in the way you expect. The data is present, you'll just need to adjust a column or row to fully display the data.
Date fields may display as #######.
To see the full date and time, expand the width of the date column.
Fields where there may be a list of items, like Owners, Labels, and Tasks, may display only one item in the list.
To see the full list, expand the height of the row.