We had several reports on this and it looks like the video engine of Dorico is eating up way too much cpu time. We are still under investigation, but for affected users a temporary workaround could be - at your own risk - throw out the video engine from Dorico’s component folder. But as said, do at your own risk and also make a backup copy of the Dorico app beforehand.
And yes, the video engine might even go berserk with projects that don’t even have video attached to. We will get to the bottom of this.