HTTP status code -1 mean?

I am using openshift which contains Haproxy2.0 as route LB, recently, I got several 502 from frontend nginx. When I dig into the Haproxy log, I found:
worker-0 haproxy[355]:
...:54628 [23/Nov/2021:07:14:34.892] public be_http:des:gateway-esb-http-route/pod:gateway-esb-http-647c66b9cf-5md4w:gateway-esb-http-server::...:8081 0/0/0/-1/0 -1 0 - - SDVN 13/3/1/0/0 0/0 “POST /esb/api HTTP/1.0”

for sensitive reasons, I hid the IP information. My question is, what does the HTTP status code “-1” mean? I didn’t find any useful information in http://www.haproxy.org/download/2.0/doc/configuration.txt. From the log, the only thing I can get is the server closed the connection, but how?