Displaying "tooltips" in Highcharts
My observations thus far:


You are not actually using mouseenter in your code, you should as that would be the better approach
The function inside a loop with the double var assignment is awkward, if you want to go functional just use .forEach()
The way you have // handle this if needed, the reader is not sure if that can happen. If it can happen, then the code will create 2 times labelElement since you did not call labelElement.destroy(); in that else branch. If it cannot happen, remove the code. Also if it cannot happen, place labelElement.destroy(); after the if statement
labelElement seems to be a global, I hope it is created with a var statement elsewhere in your code
From a naming perspective (not sure this is your naming), I have no idea what scrollGroup would return, and even less of an idea now that I see that that object has a method called translateY. You might want to re-consider carefully some of the naming.