Drag and drop feature in Custok menus has gone!

Hello,

I don’t know what i have done, but yesterday i could drag and drop the links in my main custom menu to move them and nest them where i wanted.

Now the bars for each link are not able to be dragged and dropped, but have arrows to move them up and down!

see this screenshot:

https://www.lucyryderwebprint.co.uk/custom-menu-ordering.jpg

Does anyone know how to switch back to drag and drop mode?!

I am on 3.2.1

Cheers!
Lucy