I have completed the Dungeon in both Seasonal and Eternal.
According to the Challanges, this dungeon is meant to grant the base Aspct of
Momentum. However this has not been granted, and the Challange cannot be completed.
The Codex however does not list the Dungeon as granting the Aspect and indicates that a piece of equipment must be salvaged.
Please correct the Challange to not include the Aspect of Momentum.
If you had salvaged an item with the aspect of momentum prior to completing the dungeon, then you will not get credit for it in the Challenge. The dungeon does give you the aspect if you do not already have it. Once you get the aspect, only salvaging a higher tier item will allow you to upgrade the aspect. That is why is indicates that a piece of equipment must be salvaged.
I thought this too, so I tried it on Eternal where I have not played SB. Did the dungeon with my Sorc and was not credited with either the aspect or the challange.