Originally just widescreen conversion and some QoL updates. They very quickly realized a couple things. One whole thing needed to be reposed and it was going to take more than a couple months like they figured. Two the rig system they'd used for posing the last few years isn't very user friendly. Three the code needed major surgery instead of their tried and true method of plastering it with band aids and hoping that'd magically fix the problems.
So Stray built a new rig system, so they had to re-export all 15k of the games assets, it turns out DC sucks at naming them and they have no clue where anything is. So they had to go through all 15k assets one by one to re-label them in a consistent manner, Oops DC was a lazy idiot who half assed a ton of assets and they all needed to be fixed.
So once all that was done they started reposing the game, while Stray started major surgery on the codebase in essence this is now a full rebuild of the game.