1.

The reason why the device is jailbroken is because the jailbroken fruit powder usually uses an unofficial way to install the App instead of using Apple.

ID download, directly "hard" plugged into the device.

2.

There are multiple apples on the application on the device.

ID account association, used in every apple.

When the ID downloads the application, something similar to a digital signature will be applied inside the automobile supply and demand. For example, your device is logged into A's Apple.

ID, the apple that used to use B.

ID downloaded the app, and maybe even synchronized C's Apple.

ID account information, such as iCloud, etc., such devices are prone to inconsistent signature detection and easy to flash back.

3.

Now, either there are some problems in the specific app, some apps hide some problems more or less, or the stability of the app is not good, and some operations that cause problems such as jamming will lead to flashback.