I had the idea that the issue might be caused by the relatively low frequencies used in the tests, like maybe a new note only starts when an already running wave/period finishes. But using high frequencies like :f5 does not change anything either.
EDIT: Further, I tried to control different opts, still with sleeping between play and control. It appears that cutoff (top) changes with a delay, while amp (bottom) does not (or at least less delay than the length of the tick sound, here 0.03):
