Downgrading your server from 1.11 to 1.10 will result in various issues including no spawners working, disappearing, etc. (upgrading should work fine though).
Config files won't migrate automatically when you upgrade the server to a new major version. This will be fixed in 3.0.
If a config value doesn't exist it will toggle between that value and all values in the config every time the plugin is reloaded. Pushed back. Will be fixed in 3.0.
