When exporting keyword data export bids including default bids instead of leaving it blank.
I included a CSV file of an account but deleted keywords, ad groups and campaigns for anonymity. Notice that under the bid column there are blanks where the default bid should be. This would be useful when using a formula in a spreadsheet to calculate bids. You can't use a formula on blank cell.
Admindareo (Product Manager, Bing Ads) commented
Can you provide more details on whether you were using the Bing Ads Editor or the web interface to perform this export?