This error is quite weird.
That configuration is for nginx, this image uses apache, and for apache it is not needed.
That is configured too as indicated here: https://guacamole.apache.org/doc/gug/proxying-guacamole.html#tomcat-remote-ip.
But I have found an issue with that in this scenario.
Could you try this workaround, edit
/opt/bitnami/tomcat/conf/server.xml and look for this group of lines:
and replace the interalProxies line by:
and restart tomcat.
sudo /opt/bitnami/ctlscript.sh restart tomcat
There should be not any difference at all, but we will check why is happening this.