My object is a single mesh, all extruded from a cube, no joined objects.
I've made an array of them in x and y, making sure to keep them separated and not touching each other.
I've applied the arrays, then selected all the objects, gone to Edit Mode and pressed p to separate - selecting “by loose parts”
Applied a rigid body, type = passive to the ground plane, and "active" to the falling objects.
I've tried the objects at 1kg and 0.1kg, and adjusting the friction on the active and passive objects, but I get the same issue - the objects are swirling into a kind of weird vortex?