filter on sheets mobile (iOS, iPadOS) does not work

filter on sheets mobile (iOS, iPadOS) does not work

I have this issue on every spreadsheet, whether imported or created natively in Zoho Sheets. I can use on desktop without issue:

desktop screenshot
on iOS the filter dropdowns are not there and there is no way to add them 
mobile
iPadOS looks the same as iOS, but it does have the filter button on the top. however, when I click it, I get an error: "Please choose a valid range to apply filter."

I had thought maybe it was not working because I was using an imported spreadsheet, but that is apparently not the case. What can I do to resolve this? Not being able to use the filter function on spreadsheets on mobile defeats the purpose of using mobile apps.