As of my latest testing from 18/10/18, highlights don't work on (modded?) servers. Settings also do not stay changed except if edited via the .cfg file.

To add to this, some settings are actually missing from the configs, so editing the configs doesn't even always work around this. :(

The "Include Twitch Smileys" setting being one example.

Closing since 1.12 is no longer supported and the eventual port to 1.16 will have a rewrite of the configuration that will solve this on its own.