I was riding along yesterday and it seemed I was hitting a threshold where my avatar couldn’t decide if he wanted to sit on the seat or get up and stand. I don’t know how your algorithms work but maybe rather than a single threshold, overlapping thresholds will prevent a jittering avatar.
I also have some issues concerning when my avatar stands up.
I sometimes standup at very low cadence during the rest intervals of erg mode workouts. Even though my cadence is in the 40’s, my avatar does not standup. The resistance at these points is very high even though it is a rest segment.
The Avatar stands up if the gradient is above 3% and your cadence is below 70. Now riding up Zwift Mountain over the long bridge, there is a section where the gradient is right around 3% and the avatar sits up and down all the time.