There are two different types of "Priority". One is for conventional systems, which is called "Priority Scan Mode" and the second is for trunked systems, which is called "Priority ID Scan".
What you see is associated with the conventional system priority. There are two settings, one is in the Profile editor until miscellaneous settings, the second setting is to select a channel/frequency to be the Priority Channel. Once you have made those settings, your scanner will need to "see" the channel assigned as the priority. It cannot be Avoided (either the channel itself, the department or the System) or the Department/System/Favorites List Quick Key off, or be off due to Location Control operation. Another thing would be the Service Type for the channel to not be enabled.
Lots of little stuff to check.