When I try to edit an Individual Landing Page I get an error:
Attempt to clone or unapprove the page shows the same error. Does anybody have an idea why it happens or what can I do to fix it?
Have you tried logging out and logging back in and try and clone the asset.
Usually, you receive errors when you try to edit an asset that is in a shared folder. Specifically one of the sharing destinations rather than the source folder.
I think this is a different scenario. If the issue doesnot resolve after you log back in, i would suggest you to raise a ticket with support.