Nick
Not a Ryanair crew member, but the same procedure exists at Jet2.com where I work.
Basically, the cabin crew advise all secure, but occasionally they then have to get up again after passing the secure, and don't have an opportunity to advise the flight crew. This PA then gives them the final notification that landing is imminent and that they must return to their stations and strap in, or advise the flight crew that the cabin is no longer secure and the approach will then be terminated until the cabin is once again secure.
Hope this helps your comprehension.