The GDA has had it's fair share of weird happenings. Jack is one of them. He only ever returned on Halloween during the TB era.
We haven't seen him ever since Revenant was defeated.

Scenario 1: Return of the King

Scenario 2: TB Force's Railgunner POV.

Scenario 3: TB force's Railgunner POV Alt.

Scenario 4: Overseer Prime vs The King

Scenario 6: WAR MACHINE vs The King

Scenario 7: Void Traitor & The King

Scenario 8: Blank.

//OOC because theories.

//I believe that Jack and King Jack and Expired Jack are the same fellas, and the leaders of the old calamity/the enemies in the Shattered Moon divergent timeline.

//The TB Forces and GDA were separate, but allies, they merged after the deafeat of Revenant in TB winter 2021.

//The first ever event in the TDX timeline is the fight with the original Jack, since wave 0x7 is going to be another prequel and one of the first events in the timeline, Expired Jack appears in it, sort of implying that Jack had to be killed before 0x7. Which, by my standards, mean TOWER BATTLES Halloween 2017 is the first ever event in the timeline.

//TB Winter 2021 / aka Revenant's army's attack was the last event in the TB era.