This article describes how JTAC resolved the VPN tunnel which was down.

Upon checking the inactive tunnels, could see the below reason:

@us-iad4-ofw1> show security ipsec inactive-tunnels

 Total inactive tunnels: 2

 Total inactive tunnels with establish immediately: 0

 ID      Port  Gateway     Pending SAs  Tunnel Down Reason

 131074    500  x.x.x.x  1

  Tunnel is ready. Waiting for trigger event or peer to trigger negotiation  (1 times)

 131075    500 x.x.x.x  1

  Tunnel is ready. Waiting for trigger event or peer to trigger negotiation  (1 times)

The configuration for the VPN tunnel is complete, and it is in a standby state. It means the tunnel parameters (such as encryption, authentication, and peer information) are set up.

Once the interesting traffic is detected, the system will start the negotiation process to establish the secure tunnel between the two endpoints.

Initiate interesting traffic to bring up the tunnel.

or

Configure the below:

set security ipsec vpn <vpn-name> establish-tunnel-immediately.

Hence the tunnel will not wait for any trigger event, instead it will bring the tunnel up immediately once configuration is done.