Hello @Jake_Carithers and welcome to Discussions!
If I understand it correctly, you unable to complete the mission "Holy Day" because the mission has not appeared in their mission log after completing "Kingdom's End" ?
If that's the case, could you try reloading a save prior to completing "Kingdom's End" and try again to see if the quest doesn't appear again?
Should the issue still persists, I would kindly ask you to record a short video showing the issue and the game version and send us a link so we can investigate this further. Please also make sure that your latest saves are ...