I started my server with the latest version of EpicWorldGenerator and EpicNetherGenerator but I had this error in my logs.
My server is running under Paper and is in version 1.13.2.
I still managed to create the map without error but I think it still misses some things in your plugin and where this error. I also take this opportunity to transmit this image that clearly shows several "holes" and lack of lava in some places. Hoping that you will be able to correct this quickly and efficiently.
And I forgot to tell you that the fortresses of the nether are not generated, I found none ...
Even better, complete crash and chunk errors: https://hastebin.com/katihexehu.rb