My config:

    "uranium-92": {
        "biomes": { 
            "excludes": [ ] 
        },
        "blocks": [
            { 
                "chance": 100,
                "name": "modernmetals:uranium_ore"
            }
        ],
        "dimensions":  [ 0 ],
        "enabled": true,
        "feature": "normal-cloud",
        "replaces": "minecraft:stone",
        "retrogen": false,
        "parameters": {
            "attempts": 4,
            "frequency": 100,
            "maxSpread" 3,
            "maxHeight": 48,
            "minHeight": 32,
            "medianSize": 13,
            "variation": 0
        }
    },

Result: No ores spawned.

you told it to spawn a variant of the ore that doesn't exist, so when it got back a null, it discarded the spawn

Work has been done - does the latest Maven code have this fixed ?

Testing shows normal-cloud functional - closing