Barring any other issue or network problem, try these changes to two configuration files on all systems: 

1)  adding the following to the "http" section in /var/opt/silvertail/etc/nginx-scoutproxy.conf on all systems :

proxy_buffering off;

2) The same line should probably also be added to siteproxy.conf to be safe.

3) ScoutProxy should be restarted with a sighup

kill -1 `cat /var/run/silvertail/scoutproxy.pid`

Notice the tic marks here are the ones below the USkeyboard ~ character, not quotes or single quotes.

This causes scoutproxy to reload it's config file only.