Hi.
Could you try SG v6.8.6 with Kibana v6.8.7 and let me know (in the current thread) if you have some issues?
You need to download SG v6.8.6, unzip the archive, change the version to 6.8.7-19.0 in package.json and move the unzipped plugin to kibana/plugins/searchguard.
Detailed instructions (Linux, OS X):
cd ~/Downloads
wget https://releases.floragunn.com/search-guard-kibana-plugin-6/6.8.6-19.0/search-guard-kibana-plugin-6-6.8.6-19.0.zip
unzip search-guard-kibana-plugin-6-6.8.6-19.0.zip
sed -i.bak "s/6.8.6-19.0/6.8.7-19.0/" kibana/searchguard-kibana-6.8.6-19.0-SNAPSHOT/package.json
mv kibana/searchguard-kibana-6.8.6-19.0-SNAPSHOT path/to/kibana/plugins/searchguard