oh, so I'm not the only one I guess.
Additional information: I think is related to the intrigue decision during the pilgrimage. the times it happened to me were always when I used the intrigue optionsa due to having 10+ intrigue.

Had the same issue but I think I tracked the cause of mine down. The Pilgrimage breaks if I raise levies/ create a new retinue during it without having the character's ability to lead an army disabled, the little shield icon. Not had any issues with the intrigue decision, perhaps multiple causes?