I don't have my 550b press grounded, nor do I really see any benefit in doing so (just my opinion)....
What I do know from previous years of reloading:
If you go too fast, and don't allow that extra smigeon of time for all of the powder to fall through the powder funnel...... you WILL get powder spilling as you lower the shell plate.
My advice: SLOW DOWN...... Allow the powder to fall completely. That's even more important in the rifle calibers... My 30-06 and .308 load require twice as much powder as the 5.56 rounds, and it takes twice as long for that powder to fall through the powder funnel. So, when I am doing my reloading, I pause just a bit at the top of the stroke.
Keep in mind that any and all powder that you see on your shell plate is powder that DIDN'T make it into a cartridge assembly...... when it was supposed to.......
Whether you have good eye/hand coordination, or are an old salty dog (for Bob's benefit! haha) like me, the press can only be operated at a given speed, mostly determined by how fast the powder will drop, and not any function of how fast you can place components.
So, slow down and see how that goes. Go for quality rather than quantity.