Keyframes become unmovable

MartinNewmark Posts: 19 Just Starting Out*

I have two video tracks (one of me, one of my desk) that were recoreded at the same time and I'm using Opacity to fade from one to the other. At a point, the keyframes become un-moveable by pressing and dragging them. If I shut HitFilm down and restart it the keyframes become moveable again. Do any of you know why the become un-moveable? Thanks, Martin