I had a problem where the first boss of Vesper's Host became softlock after we got him down to where he was supposed to split off. Instead, he teleported back up and then again back down with the immune shields on him. I believe it's because it took a chunk of damage when it was reforming, but I am unsure. After wiping, we were able to proceed but I can see that it could cause delay if possibly done in a flawless run.