servent of decay unique not working on mercenaries

When equipping the Servant of Decay unique chest on my mercenary (Ranger), the expected Void Spawns are not being summoned every 4 seconds, as stated in the item's description.

Reproduction Steps:

Equip Servant of Decay on a mercenary (specifically a Ranger).

Enter any combat zone or idle area.

Observe for the Void Spawn summon effect.

No Void Spawns are summoned, even after extended time.

Expected Result:
Void Spawns should be summoned automatically every 4 seconds as described, regardless of whether the item is equipped by the player or their mercenary.

Actual Result:
No Void Spawns are summoned when the item is equipped on a mercenary.

Notes:

Tested on multiple zones and instances.

Effect works when equipped by the player character, but not when used by the mercenary.

Bug may be limited to mercenary interactions.