I have a Lyon and Healy Prelude that I’ve had for about 4 and a half years and I have the exact same problem! It’s not so bad on some levers, but I have problems playing at recitals on my own harp because they continuously fall down. I have asked about finding replacements for them but apparently the Loveland (I think that’s what they are) levers arent sold by them anymore. There is supposed to be some kit that you can buy to tighten them, but it’s a total waste of money. It doesn’t help at all.