Is this Garnish message bad? "Element was added to more than one selector"
That message comes from from Garnish.Select, when the same DOM element is associated with two separate Garnish.Select instances. The JS will log that message right before destroying the first Garnish.Select instance.

It’s not necessarily a bad thing, but could be an indication of something in your JS that could be improved. (Craft’s own JS causes several of those messages, so don’t worry too much about it if everything seems to be working correctly.)