Dropped songs

My Apple Music library drops songs spontaneously. I only discover this when I go looking for a particular song. These songs disappear from my personal playlists and I don't know it until I hunt for a song in my library. Can this be corrected, and if so, how?

Secondly, in all previous versions of iTunes the scroll-bar on the right side of the screen could be clicked just above or below the position marker and the library display would move 1 page (20-30 songs). In Apple Music this does not happen. I have almost 20,000 songs and when I try to move from page to page in the whole library I have to move the scroll-bar a tiny amount which is very tricky. Can that feature be re-activated, and if so, how?

Thanks.