Recently ran into a bug in Fate of Iberia with Contract Assistance. If you sign up to help another ruler with their war and the ruler you are contracted to stops being part of the war, but the war continues with a different ruler (in my case because the target duchy of the war became independent from the kingdom I had contracted assistance to), you leave the war with no notification and the Contract Assistance options becomes forever bugged, saying "You are already Contracting Assistance in a war."