Hi @fb1
the zoom which you are removing is the default widget which automatically gets created while creating view and that is why you have passed it in double quotes.
And the zoom which you are adding is your new instance of zoom widget which is separate from the default one..
here no need to create a new instance. Just remove the already created zoom instance and add it back..
view.ui.remove("zoom");
view.ui.add("zoom", "top-left");