Hi @dyross, thanks for the project, I also forwarded it to Daniel.
On a separate note, though it might also play into your other issue, the project file is very big and the major part of all the data is audio engine data. To be more precise, it is plug-in data. When saving a project Dorico asks each plug-in to save its state and then it collects all these data chunks. The data is proprietary to the plug-ins and Dorico does not interpret it. In your case, you have the Youlean loudness meter, which creates data chunks of really massive size. So you either go to the Youlean settings page and switch that off or - even better - try to not use that plug-in at all. Btw, here is a little further info on that.