My best guess is that ND simply can't string plays together. It's not about subtle tactical shifts, it's about basic execution. Fortunately we have an elite pass-catching TE who can bail out our passing game, but beyond Mayer it seems like there is no passing game. Or at least not a serviceably reliable one. And certainly not a prolific one.
Is that Buchner's fault? I don't know, I wouldn't think so. I'd be much more inclined to think our struggles are more holistic.
If I was Rees and I was scrambling to come up with some philosophical shift to jump-start things, I would abandon the run and start leading with the pass, which is what ND has always done, and let it open up the running game. Just like we did under BK. And lean on what you know and what works.
But ultimately it's not hard to visualize this offense struggling to consistently move the chains, and march up the field, regardless of the particular strategic/tactical approach.....