Students who learn about dubitante opinions sometimes ask me how they differ from concurrences. I typically tell them that, generally, a dubitante is no different that a concurrence with reservations.
Here's a perfect example. Judge Berzon joins the judgment. She just wants the Sentencing Commission to change (and make clear) the rule that she'd prefer.
Which is totally fine.
But there's a judgment. One from which she doesn't dissent. Hence she concurs.
Or at least that's my (overly binary) approach to the thing.