Request Invasion CB no longer valid

[The Roose]

So i started at the Iron Century Bookmark playing as Normandy. I managed to get a Request Invasion CB granted by the pope so i took my time, built up my army and waited for the year 1016 just for some role play cause why not. So at 1016 I launched my invasion and it was going well. My 7k army beat the English 7.5k army at Essex and my warscore was around 60 percent, however, all of sudden my Invasion CB became invalid.
Neither my character nor the English king passed away so i am not sure why the CB ended. The only notable change during and after the CB ended was my French liege suddenly died of illness.
Does the death of one's liege lead to an end to the Request Invasion CB? If so, why? I got permission from the Pope not the King of France

[TehJumpingJawa]

My guess is that the war target (or you) changed religion.

As the invasion CB is granted by the Pope, it'll be invalidated if one or other of the participants no-longer has the Pope as their religious head.

Another possibility is that your new liege changed the realm/crown laws (enacting Absolute Crown law in vanilla CK2, or making Vassal War Declarations illegal with the Conclave DLC).

Though given the stated date, the latter seems unlikely as the tech level necessary (Majesty 5) is unlikely to be achieved so early by an AI ruler.

It's worth checking the message log ("+" sign below the mini-map, to the left of the Chronicle button), as that often gives a better explanation of why a CB became invalid.