There is a problem in my webserver. When I put the configuration ProxySet disablereuse=off many access in my website return 503. When I remove this configuration, the website access normaly. Why? Ok, the default configuration is OFF, but why when I set this configuration my website doesn't access?

Apache version: 2.4.12  MPM Event

<Proxy fcgi://>
ProxySet timeout=90 connectiontimeout=90
ProxySet disablereuse=off retry=0 keepalive=off ttl=1
<FilesMatch \.php$>
SetHandler "proxy:fcgi://"