Why are labels not showing up in my coworker’s sidebar?
The idea is that members of an organization may have different responsibilities and be interested in different labels. Listing all labels in everyone’s sidebar by default may feel cluttered for those interested in just a few labels. We automatically show newly created labels in the sidebar for the person creating the said label, since they are likely to be interested in it.
Everyone can easily manage labels as they see fit: hidden labels can be opened by clicking the More button just above opened labels, and can be hidden again by hovering and clicking the X button as shown here: