This is all very strange. From the spindumps I can’t really see what is going wrong.
But one tiny detail I’ve noticed, which as well could be decisive, but also could be not.
Your mediaclient bundle is one update behind. So please update to the latest by once opening the Steinberg Download Manager. The Download Manager will try to update itself as well as the common Steinberg system components to which the mediaclient belongs. So after once running the Download Manager, try again in Dorico to create a new project, then save it and reload. Getting any better?
If not, then we need to further elaborate on it. So please take that saved project and strip all the audio engine data from it. A corresponding shell script and instructions can be found here. If stripped down, does the project then load without stalling?