nginx: connect() failed (111: Connection refused) upstream

2024/12/02 03:14:55 [error] 812#812: *1042 connect() failed (111: Connection refused)
    while connecting to upstream, client: 10.0.0.44, server: api.example.com,
    request: "GET /v1/status HTTP/1.1", upstream: "http://127.0.0.1:8080/v1/status"
2024/12/02 03:14:55 [warn] 812#812: *1042 upstream server temporarily disabled
    while connecting to upstream

app logs show nothing since 03:10 — no crash line, just silence.
systemctl status app says "active (running)" but port 8080 is closed.