If you have enough manpower but cannot replenish soldiers.
when you have this problem and the population cannot grow
This means that there is a mod you are using that overrides the on_action keyword quartery_playable_pulse in vanilla game, .
it's a serious conflict that will not only cause the quarterly effect on which WoC relies to fail, but also override the quarterly triggering events in vanilla game.
Check all mods that use quartery_playable_pulse, If they use the following code:
quartery_playable_pulse = {
trigger = {}
effect = {}
}
they should not use effects or triggers here
the mod is the cause of the problem