Which style is this move from?

[Jimbo]

As RenDaHai has stated, this movement is in countless systems and is not particular to any one style.

The way this movement (or concept) often appears in forms does not mean it's designed to be used rotating one side then the other in continuous circles. That's simply a way of practicing the movement. Combined with footwork during application, it might only be done once, from one side, followed by an offensive attack or counter.

[Cataphract]

But if you find its the transition you find weird rather than the guarding structure then I see your point.

Yes, that is what I meant.

The way this movement (or concept) often appears in forms does not mean it's designed to be used rotating one side then the other in continuous circles. That's simply a way of practicing the movement.

Agreed. It could be an abstract motion meant to teach a general principle and build muscle memory. But this argument could be applied to every move that is not obvious on first sight.

Btw., I have found an application from Tim Cartmell that convinces me. It involves blocking while attacking the floating rib and a quarter nelson.