After encountering an issue, the developer reached out to me to address the issue, looked into it and fixed it extremely quickly. In general SimpleCurrencies, is as the name implies very simple to use! It also doesn't cause any lag and has an active developer :)
This plugin is utterly awful. The config wipes itself if it's edited whilst the server is on and doesn't come with the basic functionality of a reload command to update changes efficiently. It might sound harsh, but I don't even know why you uploaded such a poorly coded, un-optimised and feature-lacking plugin.
I am looking into the issues you said you were having. So far I cannot reproduce them. If you can create an issue on GitHub and provide exactly what was being done when the issues happened, I could look into it further (also the plugin does have a reload command. /sc reload)