A couple of years ago we stripped and levelled one area of lawn and
about a year ago did the same to a second one. In all there's probably
an additional 20T of top-soil compared to when we started, from two
different sources.
Both areas were allowed to settle and then thoroughly seeded but the
grass grew in patches rather than evenly and the overall quality of lawn
is pretty awful. The first area also has soft bumps where the grass has
grown.

Any lawn experts out there? What's going on and how can I fix it?

Dave