Vault process exist unexpected

Vault version: 1.7.2

systemctl status output:
Process: 18765 ExecStart=/usr/bin/vault agent -config=/etc/vault.d/vault-agent.hcl (code=killed, signal=PIPE)
Main PID: 18765 (code=killed, signal=PIPE)

[Service]
User=vault
Group=vault
ProtectSystem=full
ProtectHome=read-only
PrivateTmp=yes
PrivateDevices=yes
SecureBits=keep-caps
AmbientCapabilities=CAP_IPC_LOCK
Capabilities=CAP_IPC_LOCK+ep
CapabilityBoundingSet=CAP_SYSLOG CAP_IPC_LOCK
NoNewPrivileges=yes
ExecStart=/usr/bin/vault agent -config=/etc/vault.d/vault-agent.hcl
ExecReload=/bin/kill --signal HUP $MAINPID
KillMode=process
KillSignal=SIGINT
Restart=on-failure
RestartSec=5
TimeoutStopSec=30
LimitNOFILE=65536
LimitMEMLOCK=infinity

[Install]
WantedBy=multi-user.target