I have trouble in zeroing my scale. The arm, apparently set to zero, if gently hit sidewise jumps to another position, higher or lower.
The "V" blocks are clean as well as the knives.
Has anybody had a similar experience?

It appears that you are canting the blades in the v block. Don't know why you'd be tapping the arm sidewise but as a matter of routine, when the arm comes to rest, I tap the table lightly to make sure everything is settled in.