https://www.polytechforum.com/materials/memory-effects-in-a-spinning-rotor-5999-.htm
Aspden observed this anomaly. A Polish physics group seems to have observed the same thing (independently?)
It looks as if the subject was ended by assertive skepticism - concerning bearings or links with earth's spin. The researchers claimed it was larger than those things and that, in fact, it varied widely according to the substance of the disc spun (teflon being greater than plexiglass)
I will try to get to a physics library to check the references closely. The relevance to overunity might involve the ability to spin a rotor up and down and collect the difference.