When I review your mesh and even when I recreate it on my own, I see the following warnings in the Mesh Log.
I downloaded your geometry file, imported in to Onshape, and then imported it back into Simscale. This seems to have cleaned up the geometry enough to work as I did not get any errors or warnings during the meshing phase.
I used the following settings for meshing.
I would use Second Order mesh to get better results.
I no longer see the Shell in the Material pick list or the tree. I only see the Volume.
Constraining the model and adding -100N force, I am able to run the simulation without any further issues.
Here is the project I modified.
I hope this helps.