You can drag songs with the left mouse button to rearrange them. If that doesn't work, there are 2 possible reasons:
At the very top of each playlist you can see sorting columns that can be clicked. Once a sorting column is activated, you can no longer reorder tracks freely.
To change this, lick on the activated top column until the green sorting arrow disappears. After that, you should be able to reorder your playlist manually again.
You can only rearrange tracks inside your own playlists.
Workaround: Copy the user's playlist
After that, you have all songs in your own playlist and you can rearrange them.
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