Jepp; I do keep the reservoir fairly full. Only throwing 4 grains makes it easy to stay consistent with that. The measure is mounted solidly to my bench, which is rock steady. Also, I have my drops down cold. Same motions and pressures.
Scale is calibrated at the start of each session (it's digital), and I check it during the session with a test weight.
Mac; All parts are tight. It's a pretty straight forward design, which is one of the reasons I bought it. I did break it down for a good cleaning after the problem started, so I know everything looked good inside.
The only "odd" thing that I can think of is that the powder seems to have developed some static cling. It sticks to the plastic funnel, and even sticks somewhat to the metal pan on the scale. This is a relatively new thing.