Cached plugins not working (cache not written)

Troubleshooting
3

I have no idea, I have the /etc/xinetd.d/check_mk created by checkmk, I only changed the only_from line:

service check_mk
{
        type           = UNLISTED
        port           = 6556
        socket_type    = stream
        protocol       = tcp
        wait           = no
        user           = root
        server         = /usr/bin/check_mk_agent

        # To avoid intentional or unintentional overload due to too many parallel
        # queries from one source we set this parameter. It limits the number of
        # concurrent connections per source address. If you need more requests
        # per source system, you can of course increase or remove this value
        # (https://github.com/tribe29/checkmk/pull/157)
        per_source     = 3

        # listen on IPv4 AND IPv6 when available on this host
        #flags          = IPv6

        # If you use fully redundant monitoring and poll the client
        # from more then one monitoring servers in parallel you might
        # want to use the agent cache wrapper:
        #server         = /usr/bin/check_mk_caching_agent

        # configure the IP address(es) of your Nagios server here:
        only_from      =  xxx.xxx.xxx.xxx 127.0.0.1

        # Don't be too verbose. Don't log every check. This might be
        # commented out for debugging. If this option is commented out
        # the default options will be used for this service.
        log_on_success =

        disable        = no
}

I never did anything else and they always worked, is there something else to do?