The problem is caused by invalid mixin definition, the "ServerMixin" (i assume) should be server only:

"server": [
    "ServerMixin"
 ]

in weeping_angels.mixins.json, i can't tell by looking at that class if this is fixing the problem or only the symptoms.

And about the missing OroConfig - the build.gradle looks ok, maybe check if you uploaded the right file to curseforge (the one without the -dev and -sources at the end) as that could also explain the mixin problems.

Thanks! I'll get right onto fixing that tomorrow
Sorry that this happened

This should have fixed it: https://www.curseforge.com/minecraft/mc-mods/the-lonely-assassins/files/3223802