The mobile app wallet being closed source may bring the following potential risks:

1. **Security Vulnerabilities**: Closed-source wallet applications may not have been reviewed by third-party security experts, thus there may be undiscovered security vulnerabilities. These vulnerabilities could be exploited by hackers, leading to theft of user funds.

2. **Privacy Leakage**: Closed-source wallets may collect personal data without the user's knowledge, which could include transaction information, contact lists, device identification information, etc., posing a risk of privacy leakage.

3. **Malicious Code**: Since users cannot view and verify the code of closed-source wallets, the possibility of the wallet containing malicious code, such as backdoors or monitoring software, cannot be ruled out.

4. **Dependency Risks**: Users of closed-source wallets are entirely dependent on the updates and support provided by the developers. If the developers stop maintenance or the project is abandoned, users may find themselves in a difficult situation.

5. **Lack of Transparency**: Being closed source means users cannot know exactly how the wallet operates internally, which may lead to doubts about the wallet's security and credibility.

6. **Trust Issues**: Users need to fully trust the developers of closed-source wallets since there is no open code review to validate the wallet's security and correctness.

7. **Malicious Developer Actions**: Developers of closed-source wallets may deliberately embed malicious features in the code, such as hidden transaction fees or unauthorized fund transfers, which users cannot detect through code review.

To mitigate these risks, users should consider choosing wallets that are open source and have undergone security audits. This can ensure the wallet's security and transparency. Additionally, users should pay attention to protecting personal information, regularly update the wallet application, and use strong passwords and two-factor authentication to safeguard their account security.