Saw that they updated the Face AR Sample to 4.26… downloaded to see if this was fixed. Still can’t select the “Update Animation in Editor” button, but you can see it update in the preview viewport of the KiteBoyHead_JointsAndBlends_AnimBP class. Also, when you play the project, it also updates. You do have to save and compile the AnimBP after linking it to your iPhone.
Oh yeah, I also had to make the Z (Yaw) value of Make Rotator positive instead of negative, because it was inverting my head movements otherwise.