Looking at this, it might be because you are experiencing joycon drift. My girlfriend had joycons and we decided to fix them together. When they arrived we replaced the broken joystick body with one of their own, put it back together and attempted to recalibrate it. The new joystick has already drifted! We were able to disassemble the entire joystick assembly and clean the 99% IPA sensor and it now works perfectly. But we could save money and just do it with the original joystick assembly. The only difference is that we had a backup in case we made a mistake. Leaving 3 stars because it works fine now, but you might need to fiddle around a bit. That's probably fine with you if you're looking for a replacement joystick and not just shipping your joycons to Nintendo. Also, I never tested the second joystick that came with the kit, as far as I know it works perfectly.