We are sorry for the inconvenience and want to resolve this as soon as possible. Our initial guess is that this is related to background noise. We have chosen to set the sensitivity at a high level to allow as precise tuning as possible. A high sensitivity will make the tuner react to the background noise and the needle will flick around. Please try to keep the phone closer to your instrument if there is background noise while tuning.
We will add a sensitive setting in coming releases, so you can adjust it when you are trying to tune in a noisy environment.
Also, please try to restart your device to make sure the phone's systems are fresh and clean.
Please try this and get back to us if you still are experiencing issues or have any questions. You can reach us here or at firstname.lastname@example.org.