I have a couple of questions (because I do not shoot long range) and a suggestion. Are you testing at a shorter range for longer? How broad are the nodes that you normally see? The reason that I ask is that I have tuned balance scales to the point that it is easy to see a half of a tenth differences (with magnification), and I have a scale wind protection box, made from wood, that has a sliding tempered glass cover (Plastic caused static issues.) and leveling feet. It has a trickler that is inside the box with the scale, but which has its handle sticking out through a close fitting hole in the end of the box. This combination does not have the drift and stability issues that are common to electronic scales when they are used in unsuitable environments, and it is quite responsive when trickling up a charge. The reason that I asked about the distance that you are testing at is that as I understand it, the importance of minor differences in charge weight increases with distance, and if you are testing at a shorter distance than you might be able to tune with something that is not quite as accurate as the digital scales that are commonly used for preloading match ammunition. That way once you had a load, you could reproduce it to tighter tolerances loading at home. I think that any scale that is sensitive enough (.01-.02 gr.) for the top level of charge weight accuracy that is preferred to minimize your extreme spreads, will be a pain to deal with in the field, precisely because that sensitivity requires a more stable environment, while those that are more stable, may be less sensitive than my tuned balance scales, and slower to trickle with.
I have tried a Gem Pro 250 that belongs to a friend,(tough not at the range) and found it to be an excellent value. I did not use it to trickle charges or load, but rather to evaluate my powder measure technique. If yours is acting up, I think that I would contact the people that you bought it from and see about returning it under warranty. One trick that I use with electronic scales is to make up a test weight that is close to the weights that I will be using plus the weight of the pan. That way, if I have a question about the reading that I am seeing, I can remove the pan and charge, and put the check weight on the scale to see if there is a problem.