Description:
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fcgi_accept_request function is supposed to call a FastCGI implementation's on_accept hook when entering an "accepting" stage (that is right before calling "accept"). This hook implementation (fpm_request_accepting) updates a worker state to an "accepting" state which is effectively an "Idle" state, and updates counters on the scoreboard of the corresponding pool (idle++, active--).

But this is not done when listening for client connections on a named pipe on Windows platform. In that case a combination of ConnectNamedPipe/WaitForSingleObject is used (to be able to catch in_shutdown as far as I understand), but it is nonetheless functionally equivalent to "accept" call. Also by not calling on_hook neither a worker's state is updated to "accepting" state nor scoreboard counters are updated.

So I suggest calling on_accept hook regardless of "named pipe" vs "tcp/unix socket".