For me, it’s the wedding scene. My original plan was to have Corrine and Alex married by the end of the first chapter, but pacing consideration and production reality turned it into a 6 to 10 chapters ordeal. Luckily in the process of figuring the scene I was able to include important information that I originally planned explaining later and include a bit of characterisation for the main cast.
When I finally reached the scene in question I had to split in two for pacing reasons, rewrite major sections because I had not achieved my narrative objective, and shuffle things in the timeline so the two parts would be equal in amount of work. (Half of the scenes take place in a small room with a cast of 3 and the other take place in a gothic cathedral with a large crowd.)
Actually, for me the scene is still not done, the first part of the wedding should be released on the 7th of April with the second part that I have not finished drawing releasing in Mai.
You can read the chapter right before all that stuff here: