Unable to drag songs from library and into playlists

So I don't use Apple Music. I'm still an old-school regular old iTunes user. As of today, when I go to drag a song(s) from the library (under songs) and move it to a playlist on the left hand column it gives me a red anti symbol and won't let me do it. I have noticed that I can copy and paste a song(s) into the playlist, but even then I can't re-arrange the order in the playlist. Does anybody know why this is happening? I've read some threads and they all seem to not work or be unrelated. For example, it's not that my playlist order isn't set to songs. It is. Any help please? I have a very particular system that I like doing and this is distressing to me. Thank you!

[Re-Titled by Moderator]