Dynamic backend not taking traffic after 10s

I have a setup where some backend come from config, and then I add various backends on the fly using the socket api with infos coming from my cloud system.
I use the triple add server …; enable server …; enable health …
Once the backend is effectively UP, I see approx 50 request going to it for 10s, and then no traffic is selected to be send there.
I tried leastconn, roudrobin and random for balance with no difference. The weight is fine.
When querying server state the old and new show up identical.
Did I miss something in configuring my extra backend ?

I’ve found my server state is 4
srv_check_result: Last check result (FAILED/PASSED/…).
Check reports the server doesn’t want new
I followed exactly this example.

I even tried to set server XXXX state ready and set server XXXX health up it still doesn’t take traffic.