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The reasons for frequent signature loss of Apple-signed apps and the measures to avoid them can be summarized as follows:

### 1. Cause investigation

1. **Certificate expired or revoked**:

- The validity period of a developer certificate or push certificate is generally one year. If it is not updated in time or the certificate is revoked by Apple, the app will lose its signature.

- You can ensure that the certificate is within its validity period by checking the certificate status regularly.

2. **Device time is inaccurate**:

- Incorrect time settings on the user's device may cause certificate verification to fail, resulting in lost signatures.

- Users are advised to check and set the correct time.

3. **Network Issue**:

- When downloading or updating an app, network issues may prevent the app from properly verifying the signature.

- It is recommended to use a stable and reliable network connection for downloading and updating.

4. **System Update**:

- After iOS system update, some apps may need to be re-signed to run properly.

- Developers need to ensure that their apps are updated and re-signed in a timely manner after system updates.

5. **Apply changes**:

- Modifications to apps without proper signatures may invalidate the original signatures.

- Developers should avoid making unauthorized modifications to apps.

6. **Push service issue**:

- For apps that require push notifications, push service issues may cause app sign-ins to be lost.

- Developers need to ensure that the push service operates normally and resolve issues in a timely manner.

7. **Device UDID changes**:

- When the user's device UDID (Unique Device Identifier) ​​changes, the app may not launch.

- Developers need to consider how to deal with changes in device UDID.

8. **Application reported or violated regulations**:

- If an app is reported by a user or detected by Apple to violate certain regulations, Apple may revoke the signature of the app.

- Developers need to ensure that their apps comply with Apple's policies and guidelines.

9. **Signature Service Provider Issue**:

- Issues with some third-party signature service providers may cause the app's signature to become invalid.

- Developers need to choose a reliable signature service provider and maintain communication with them.

### 2. Avoidance measures

1. **Regular Inspection Certificate**:

- Regularly check the validity period of developer certificates and push certificates, and renew them in time before expiration.

2. **Backup Certificate**:

- Back up currently valid certificates before they expire so that they can be quickly restored if needed.

3. **Monitor application status**:

- Use Apple's App Store Connect tool to monitor the status of your app and identify and resolve potential issues in a timely manner.

4. **Provide Update**:

- When the system is updated or the application needs to be updated, ensure that the update is provided in a timely manner and ensure that the signature verification during the update process is correct.

5. **Use a stable network connection**:

- Make sure you have a stable and reliable network connection when downloading and updating apps.

6. **Comply with Apple policies**:

- Ensure your app complies with all Apple policies and guidelines to avoid certificate revocation due to non-compliance.

7. **Use professional development tools**:

- Use professional development tools such as Xcode to develop and maintain applications to reduce the risk of losing your license due to tool issues.

By implementing these measures, developers can significantly reduce the risk of app signature loss and ensure stable operation of the app.