No mob spawning in loaded worlds

[wordandahalf]

Describe the issue
No natural mob spawning occurs in worlds loaded by ASWM, regardless of gamerule settings or difficulty.
Using /swm create and manually updating the difficulty and gamerules results in a world in which mobs spawn.

Spigot version
1.18.2

Plugin version
2.8.0-SNAPSHOT (ae292c4)

How to reproduce

Configure plugin to load world with mob spawning enabled:

worlds:
    world-name:
        source: file
        spawn: 0, 64, 0
        difficulty: hard
        allowMonsters: true
        allowAnimals: false
        dragonBattle: false
        pvp: false
        environment: NORMAL
        worldType: CUSTOMIZED
        defaultBiome: minecraft:plains
        loadOnStartup: true
        readOnly: true

Witness no mobs spawning. Spawners work, but natural mob spawning does not.

Crash reports (if available)
N/A

[wordandahalf]

Most bizarre, mob spawning was fixable by covering the world with a layer of stone, removing it, and saving it. I have no idea how or why this works.
It is important to note that these worlds were made with a 1.16.5-compatible version of ASWM and were automatically updated by the plugin to be compatible with 1.18.2.