Issues with using FortiClient VPN on Android phones

Basic Information:

Device: OPPO Reno4 Z 5G

Operating System: ColorOS V12.1 (latest version)

Android Version: Android 12 (latest version)

FortiClient VPN Version: 7.4.2.0179

FortiGate Version: 7.4.7

Issue Description: When using the campus SSL VPN, the connection is successfully established, and an IP address is obtained after entering the username and password. However, after exiting the FortiClient VPN application (APP) and opening other applications, the SSL VPN connection is found to be disconnected. Attempts to resolve the issue, including using different accounts, reinstalling the APP, and configuring the APP to run in the background, have been unsuccessful, with the same issue persisting.