Another Scale question/concern

I have a GemPro250 scale. It's been accurate and consistent for the past several years, until a couple days ago. I set an empty case on the scale and zeroed it (tare button), filled it with powder and set it on the scale. It read 4.88gr. My desired charge for that load is 4.9gr. Good enough. Phone in the other room rang and I went to answer it and left the case on the scale. Call lasted less than a minute and I went back in the room. Scale read 4.66gr. No breezes, no fluorescent lights, no other electronic devices present. So I checked again. Left a charged case on the scale and after 45 seconds or so, it started drifting. I tried it with my RCBS 1500 scale and after a bit of time it does it too. I'm thinking any scale with a strain gauge load cell will have this issue when a load is placed on it for an extended period of time. Or do we think the GemPro is starting to go bad? The scales with the magnetic force restoration are mostly out of my price range though.