It is possible that the Instrument Expansion you want to use with the kit has been removed from a slot. When this happens, the outline of the Exp icon appears as a dashed line on the KIT screen (see image below), indicating that the Instrument Expansion is no longer loaded in the slot.
If you are using a V71, V51, or V31 updated to system program Ver. 2.0 or later, enable the Auto Slot Load function, or manually reload the Instrument Expansion you want to use into a slot.
Auto Slot Load: This feature automatically loads the Instrument Expansions and Kit Packs used by a drum kit into the slots. When Auto Slot Load is set to “ON”, switching to a drum kit that uses an Instrument Expansion or Kit Pack not currently loaded in slots 1 through 6 will automatically load the required data into the slots.
For more information about Auto Slot Load, see the following documents: