Unable to delete folder from Keynote app on iPhone 16e

It is my habit to transfer my media files folder from my laptop (M4) before I back up the laptop fortnightly. I move the folder to my iPhone 16e and use the Keynote app for the purpose. This week I transferred 50Gb of data. Usually all goes well. I store the data in the Keynote app until the back up is done and then I transfer the folder from the phone back to the laptop. Then I delete the data in the Keynote app. Only this week, I can’t seem to get the app to delete this folder. Any suggestions?