The Harbinger was carrying an Immobilizer when it was shot down by Autobot while it was orbiting Earth. When it crashed, it broke in two pieces and was forgotten. Later, it was discovered by Starscream, who scouted the ship's two halves and found nothing of interest to him. He failed log the Harbinger's location in the computers, but still remembered the its location.
After Airachnid informed Megatron of the valuable weapon it once carried, he allowed her to investigate the ship with Starscream. The went into a section of the ship where, Airachnid brought its computers back online to search its manifest. This also caused the Autobot's the be aware of its location and prompting them to investigate. After reaching the section that the weapon should have been, Airachnid realized that it was in the other section that Starscream was neglecting to tell her about. She webbed Starscream so he would be forced to tell her the other location. After retrieving the weapon, Autobots arrived and defeated her.