Thanks for the additional information provided regarding the bug about Dread Palace Operation not being counted toward the completion of the "Weekly PO: Set of the Empire Operations".
Our team is currently looking into this bug. I'll update you in this thread when I have more information.
In the meantime, you would normally be able to complete this Priority Objective by:
- Completing the following Operations in Story Mode: Dread Fortress or Temple of Sacrifice
OR - Defeating the Colossal Monolith three times
For visibility, I will also add this bug to the known issues list: Game Update 6.3 - Known Issues list.