My Rally RS200 are very close to my Neo 2t when it comes to AVG and NP, but there can be a difference when it comes to max power, but that’s a known issue with power meters since they will sample data at different periods and avg it out over a time frame, so the peaks will never exactly align. Unlike my dual 4iiii (ultegra), the right side was all over the place.
After reading @triggerdog’s post, I checked my battery caps and the left side was half a turn loose, right side was tight. I’m going check them every week or 2 from now on.