version: 1.12.2

occurs with any json with a curve vein, but here's mine anyways;
{
"coal": {
"type": "curve",
"angle": 50,
"radius": 5,
"ore": [
{"block": "minecraft:coal_ore", "meta": 0, "weight": 100}
],
"stone": "minecraft:stone",
"rarity": 2,
"min_y": 50,
"max_y": 128,
"density": 128
}
}

title pretty much says it, the preparing spawn area takes forever, which means there already is server lag, and once i get in, it takes forever at first, and once thats set, i consistently get over 200ms of lag, where less than 2 ticks per second are getting processed by the internal server. This is total BS. I'm flying around and the chunks take forever to generate, even though my FPS is fine. Idk how your curved ore generator algorithm works, but it seems to be causing constant server lag. Very irritating.

See #22 (comment).
You're ticking two of the three boxes for really horrible performance. In all honestly I don't know how the curve generator works either, and I'm not particularly interested in rewriting it at the moment.