FortiClient VPN Disconnects After Windows Lock (7.4.3 & 7.2 - Free Version)

We are using FortiClient SSL VPN (free version, no EMS) and facing an issue where the VPN disconnects within 1–2 minutes after locking Windows, even though the laptop remains powered on and connected to the internet. This issue was seen in version 7.4.3, and we are also experiencing the same behaviour in 7.2.x. Fortinet support could not confirm the root cause due to limited support for the free version. Has anyone faced this issue or found a fix or stable version recommendation?