Reordering spaces in the sidebar by dragging and dropping stopped working with the release of 18 April.
It works OK for me.
What browser OS are you on? Can you upload a video?
OK, there seems to be something a bit random about it working or not 
Spaces that existed before today cannot be reordered, new spaces can only be dropped above existing spaces up to a point. Not possible below that point.
fixed thank you