Re: FortiClient not working after waking up from PowerSaving Mode
Quoting from Chapter 7 in the book "UTM Security with Fortinet: Mastering FortiOS" By Kenneth Tam, Martín H. Hoz Salvador, Ken McAlpine, Rick Basile, Bruce Matsugu, Josh Mo:
If the Forticlient keep-alive message is not received when it is expected by the Fortigate, such as when the endpoint was shut down or put into a sleep mode, the endpoint information is stored for the duration of the compliance timeout idle time, after which its authentication entry is removed and any subsequent traffic from that endpoint IP address is blocked until a new endpoint compliancy check can be performed.
I think, this is also applicable to other VPN clients like Cisco anyconnect where the VPN host closes the connection because it can't renegotiate the session key.
However, try changing the Network Connections settings under Power & Sleep to "Never" in Windows 10 once and see if that helps.