Crash Report:
https://gist.github.com/Fuzzbling/0b2c7872a4c924aaf1224729315741d0

That's what I get for not testing properly. Yay.
Will fix tomorrow, as I'm already getting ready for sleep.

From a quick glance, this should only happen on the server..?
Perhaps the default initializer doesn't work well with @SideOnly?

@SideOnly(Side.CLIENT)
private EntrySetting<T> _entry = null;

While I'm no mod dev, I did find the following that might be helpful in troubleshooting this;
https://mcforge.readthedocs.io/en/latest/concepts/sides/
MinecraftForge/MinecraftForge#3066
minecraft-dev/MinecraftDev#28

There were quite a few other results using this search:
https://www.google.com/search?q=%40SideOnly(Side.CLIENT)

I tried fixing it on my laptop but unfortunately I can't setup a development environment. Apparently decompiling Minecraft takes 3 GB of RAM (well, using OpenJDK). I'm relatively sure about the cause and reason. It's just slightly weird that it acts this way. I'd assume @SideOnly on an initialized field would not cause it to be initialized, but that's alright. (I just have to get rid of the = null.)

Meanwhile, I guess I should remove the releases, as they're faulty.