Hey don`t know if this’ been cleared up, but the reason these encoders end up being jumpy/jittery, is that the grease that makes the encoder turn nicely slowly leaks in under the knob and onto the conducting material beneath the encoder, where the encoder data is read. Just open up the synth, carefully pry the small metal tabs that keep the encoder in place (after removing the knob ofc) and lift the actuator off the base of the knob. Underneath here you can swipe with a q-tip, you’ll notice how greasy the plastic disc has become. Just wipe it dry and re-assemble, encoders work perfectly afterwards 
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