Jumpy Power on steep incline

I have a Flux S. It worked fine for the first few months. Now, whenever incline exceeds 6%, my power rapidly jumps between 50-80w and 190-200w (sometimes 0w to 180w).I tried to recalibrate the power and it might go back to normal for once or twice but then comes the same issue. The power remains normal and stable on a flatter course.

I browsed through forum and didn’t seem find other similar questions. Really appreciate support how to fix it…Thanks a lot!