The origin of this tip is in the list of layers which includes all of the Xref layers (from externally referenced files) as you can see below:

My problem occurred when trying to find a specific layer amongst all of the Xref layers and other layers in my current drawing. I dont need to see all of the Xref layers because i do not usually amend them.

The expandable list of layers shows the same layers as a Layer Manager. I create a filter in the Layer Manager in order to hide them and make the list clearer to browse.

By default there is no filter that shows only the layers from the current drawing (I think there should be) but there is a way to create it.

This is what you need to type in the field Name in Filter definition to filter only current drawing layers:

~*|*

I called this filter of course Current Drawing Layers.

To find out how to filter a layer list using different symbols please check this link:
 Filter and Sort the List of Layers

My advice is to create this filter and other useful filters already in your template file.

Image below shows my filters: