Just found out that effect of velocity device is not instant, but instead has a small attack time.
Another possibility is that there is something wrong with lfo device.
Try the following effect chain and you’ll understand what I mean
http://cs.helsinki.fi/u/ssolehti/random_drums.xrns
I’d rather choose a small delay than a small attack time.
Nearly all volume based (nd other) parameters are smoothed, to avoid that rapid changed cause artifacts/clicks. So the problem is the modulation of the volume in general, not the velocity device or LFO. This is kinda impossible to avoid if you want that parameters changes/automation are smoothly applied.
Wicked beat randomizer trick in your example rns!
Instead of using velocity devices to sync the LFOs reset, you can also automate the reset function of the LFO with pattern effects. To avoid the “smoothing” attack for the volume, put them off the beats: