Well, you can take a look at this post. But I’m not sure if it helps a lot. Guacamole is working as it is supposed to on a member-server while it didn’t on a slave-server.
But I can’t really tell if this has something to do with server roles or the other apps that are installed on the slave (I mentioned samba4 but perhaps the mailserver and anti-virus are even more relevant - some indications towards this can be found with a web search).