For me, personally, it’s mostly a feeling of excessive tension in the picking hand wrist, slight difference in the attack and sound of down/up strokes, and just sluggish movement of the wrist.
I’ve stopped practising for a few days, and I’m just messing around with variations of dart-thrower and other more flextension-y wrist motions.
I’m getting relatively certain the main reason for my own inconsistency is unconsciously switching between different wrist motions while playing, with slightly different “force drivers”, I guess, the point where I feel the motion originating, and the point I feel as a pivot.
On the motion tests, I consistently get the highest speed and smoothest feeling from the “scribbling with a pen at 45-degrees” flexion/extension, but on an actual guitar body I default to a more side-to-side deviation, mostly in the radial part of the motion curve.