There is enough film to show his footwork is causing him more problems this year than last.
This often happens when a QB goes into an offseason focusing on improving one part of his game, that another part starts to regress. Same thing happened to Blake Bortles last year. If I remember correctly, Dak spent most of the offseason working on his throwing mechanics - the issue here is, if the footwork is gone, this impacts the throwing as well.
He'll need to be getting back to basics. Dak is even admitting his footwork is a problem, I don't know what more you need. Dak can "disagree" all he wants while in the same breath saying how his footwork is causing him problems.