Confirming this is still an issue 9/1/20 on MM 4.10.0 b3435 using Paper-174 (1.16.2). This is a huge chunk of the plugin that's completely useless. No items work, whether configured manually or imported. If there's anything else I can provide I'll be happy to.
So ridiculous that it has been THIS long and even on the latest versions of the plugin, every server owner I have talked to says it is broken. They are not listening? A huge part of this plugin is broken and it is so vital for so many servers.
Premium its not fixed either, tried on my friends server, what a joke! Hit them where it hurts, their wallet. I will be looking for new plugin to support.