I've found a bug that does not spawn mobs when its last_day is set to 0.

sample config:
This will only spawn minecraft:zombie
[ "zombie_extreme:clicker-100-7-0", "minecraft:zombie-1-0-0" ]

This is considered as empty spawn table
[ "zombie_extreme:clicker-100-7-0" ]

This will spawn the mobs
[ "zombie_extreme:clicker-100-0-0" ]

The-Hordes-1.20.1-1.5.4 - Forge

Just to add context, the day in minecraft was set to 8 with /time set 8d

what exactly is the day being referred by the mod? is it minecraft day? or does the mod have a different context of "day"?