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Haproxy will get 404 error for about 2-3 seconds if one of backend server down

this is the haproxy config.
defaults
option forwardfor
log global
option httplog
log 127.0.0.1 local3
option dontlognull
retries 3
option redispatch
timeout connect 5000ms
timeout client 5000ms
timeout server 5000ms

listen stats
bind *:9000
mode http

backend testhosts
mode http
balance roundrobin
option httpchk HEAD /sabrix/scripts/menu-common.js
server host1 11.11.11.11:9080 check inter 2000 rise 1 fall 2
server host2 11.11.11.12:9080 check inter 2000 rise 1 fall 2

if service of 11.11.11.11 is down, haproxy will get 503 and 404 error about 2-3 seconds( it depends inter value, if inter value is very small, the number of 404 error will be decreased).

2020-08-25T11:58:14 11.11.11.11:9080 200 POST /tsturl1 HTTP/1.1 2274
2020-08-25T11:58:14 11.11.11.22:9080 200 POST /tsturl1 HTTP/1.1 448
2020-08-25T11:58:14 11.11.11.11:9080 503 POST /tsturl1 HTTP/1.1 0
2020-08-25T11:58:14 11.11.11.11:9080 404 POST /tsturl1 HTTP/1.1 0
2020-08-25T11:58:14 11.11.11.11:9080 200 POST /tsturl1 HTTP/1.1 1503
2020-08-25T11:58:16 11.11.11.22:9080 200 POST /tsturl1 HTTP/1.1 617
2020-08-25T11:58:16 11.11.11.11:9080 404 POST /tsturl1 HTTP/1.1 0
2020-08-25T11:58:16 11.11.11.22:9080 200 POST /tsturl1 HTTP/1.1 618
2020-08-25T11:58:16 11.11.11.11:9080 404 POST /tsturl1 HTTP/1.1 0
2020-08-25T11:58:16 host1 is DOWN, reason: Layer7 wrong status, code: 404, info: “Not Found”, check duration: 0ms. 1 active and 0 backup servers left. 0 sessions active, 0 requeued, 0 remaining in queue. 2020-08-25T11:58:16 11.11.11.22:9080 200 POST /tsturl1 HTTP/1.1 645
2020-08-25T11:58:16 11.11.11.22:9080 200 POST /tsturl1 HTTP/1.1 618\

My question is : why the parameter retry didn’t work ? is it possible for the user always get 200 code rather than 400 error even when one of the backend server down ? I’m using Haproxy 1.5.18.