This is a labor type resource and the actual hours show everywhere correctly, except the gantt.

Therefore the slices are good.  Why are the hours missing from the gantt?

This was caused because somehow the task became set as a milestone.

MSP and OWB have been known to set tasks to milestones when they should not be.

Release:
Component: PPMPRM

Open the project in MSP or OWB and remove the milestone.

Other option would be to try xogging it out and removing the milestone and xog it back in.

If either of the options are not available, or do not work, please contact Clarity support.

OWB and MSP Links:

KB000124007 - MSP: Task is incorrectly marked as a Milestone in PPM even though it is not 0 or 1 day duration

KB000007476  - MSP, Tasks are Changing to 0 day Duration / Milestones 

KB000122211 - Tasks saved in OWB automatically become Milestone