After i had the same notorious midthrottle oscillations i though about locknuts and the influence they have on the motor vibrations. I tested on the bech and the results are night&day ! The stock locknuts are uneven & hole missaligned witch resulted in bad vibrations at some rpm range (midthrottle)
Hope this information helps !
Motors in question are Emax RS2205 but i am shure this problem is present on other manufactures witch use normal metal locknuts and not aluminium ones witch have less error in manufacturing.