Destiny 2 Season of the Seraph adds a ton of new replayable activities, with the new exotic quest Operation: Seraph's Shield standing out in particular. Operation: Seraph's Shield hides many secrets, some of which are not accessible until you progress in the seasonal story.
There are also hidden chests scattered all over the Seraph facility that contains Season of the Seraph gear. Here's where you can find them.
Every hidden chest location in Operation: Seraph Shield.
There are two hidden chests in the exotic quest Operation: Seraph's Shield.
Hidden Chest #1 location
To unlock the room where the first hidden chest is, you will have to shoot four scanner drones in a particular order. These drones appear randomly in one of the three locations in the Seraph's Station. They are - The entrance room of the Seraph's Station, the Geosynchronous Orbit, and the Server Room.
As mentioned previously, the drones will spawn in one of these three places. Before you start shooting them, collect the Scanner Augment and look for the drone in yellow. Shoot it, and you will notice another drone turning yellow. Shoot all four drones as they turn yellow, and you will get a short message on the left-hand corner of the screen: Drones: Disabled // Security Door: Opened (Warsat Command Nexus)
Once you have destroyed all the drones, keep heading inside the Seraph station. You will find the first hidden chest in the Warsat Control Nexus, the final room in this mission. After you have defeated the final boss and uploaded the virus, a new door will open up here, leading to a hidden room with the hidden first chest.
Hidden Chest #2 location
You will find the second hidden chest in the Engineering Sector, where you fight the two Hive Shriekers. To access this chest, you will need the Tactical Armor upgrade from the Exo Frame vendor that lets you bypass laser securities.
There's only one laser fence in this room, so you won't have trouble finding it. Cross the fence and turn right. The hidden chest will be in front of you. That's all the hidden chest locations in Operation: Seraph's Shield. Opening the two hidden chests will complete one of the week six challenges called Seraph's Secrets.