Video files? Or what type of files?

This can be common for large files such as video files since downloads are assisted by downloading from others who are downloading the same file; ie: you are downloading from their partially downloaded files. However, perhaps not so many people have the entire file completed & in shares. So the higher the download % you get to, the less hosts are available that have those last parts of the file. And those that have the final parts of the file might have their upload slots busy with others. Search for more hosts is a wise move.