Previously, it was built against Paper, so it used certain APIs not available on Spigot. It should now work fine on pure Spigot servers. Additionally, a bug on Windows servers with saving to the right file path should be fixed now.
In this update, I rewrote the plugin in Java in order to reduce the file size (it previously used Kotlin). As part of this, I updated the plugin to 1.14.1. Additionally, I added some new features, such as the ability to ignore certain materials.