Annoying Mercenary Events

[Worot]

In my last game as Poland I've conquered most of Ruthenia, Wallachia and Lithuania.
Since then, in ten years' time leader of some mercs' band has killed one of my sons, three others have been wounded and two of my daughters have eloped.
What can I do to stop those mercenary events from annihilating my dynasty?

 

[Steel_atlas]

Pretty sure it's a bug, it's basically supposed to fire if you have the dynamic mercs hired

You can get events as Venice with the not spawned transport mercs .