We need to know exactly how the stators are connected, and we do not.
Three stators. A, B and C.
Each is wired in star, resulting in 3 output wires. L1, L2 and L3.
That makes 9 wires.
AL1, AL2, AL3, BL1, BL2, BL3, CL1, CL2 and CL3.
What is connected to AL1?
What is connected to AL2?
etc
What is connected to CL2?
What is connected to CL3?
Again, it is not cogging.
The pulsating drag is due to circulating current between stators. (assuming there is not a shorted coil)
It will stop when the stators are wired together "properly".
"Properly" may not be the way you expect. Minute differences in the stators and phases can cause circulating currents, which is what you have.
There are simple solutions (diodes). I expect you are attempting to connect too many things together before the diodes.
G-