This issue is normally associated with the bug of ghosts (as well as mesmer phantasms) losing all ghostliness when the “Character Model Detail” slider in the graphics options is set to ‘Lowest’ or ‘Low’. Setting this option to ‘Medium’ or higher normally re-ghostifies ghosts.
Some have also reported having to increase the ‘Character Model Limit’ slider to ‘Medium’ or higher in addition to increasing the ‘Character Model Detail’ slider, though this additional change does not seem to be logical and may not have merit due to the ‘Character Model Limit’ slider not affecting the details of displayed models, just the amount of displayed models.
Functionality (Hover on INFO for issue description)