Excel Filter not working as expected

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Frequent Visitor

I am using Excel 16.31 on OSX 15.1 Catalina

 

I have a spreadsheet which isn't filtering as I expect. I use filtering on a lot of other spreadsheets, and they work fine, it's just this one.

 

When I go to filter the sheet, all I get as filters is the first line in the spreadsheet, and nothing beyond that.

 

I have attached the spreadsheet here in the hope somebody can find the problem for me.

 

thanks in advance

 

Charlie