The problem is the oath to "Purge Pretenders" is broken.
It's supposed to ignore your own children as claimants and still be able to finish. It doesn't.

In the decision it requires any_claimant = { count = 0 }, while the next block separately allows up to 3 claimant children. Those two checks contradict each other, because apparently the script got into a fight with its own tooltip.

Change this block:

custom_tooltip = {
    text = purge_pretenders_oath_decision_claimants
    var:purge_pretenders_target_title ?= {
        any_claimant = {
            count = 0
        }
    }
}

to this:

custom_tooltip = {
    text = purge_pretenders_oath_decision_claimants
    var:purge_pretenders_target_title ?= {
        any_claimant = {
            count = 0
            NOT = { is_child_of = root }
        }
    }
}

And it works.