Hi Philipp,
I get the same error when using the VectorL2. I'll have a closer look at the VectorL2 tomorrow.
You could also use a space with more components. This can be done with the "dim" argument.
Code:
V = L2(mesh, order=order,dim=mesh.dim, flags={"dgjumps":True})
Using your formulation it is still not working. When I switch to a formulation on the element boundaries, everything is fine. I'll check if there is an issue with the skeleton BFI's.
Attached is a file which should do what you want, using and L2 space with as many components as your mesh dimension and an element boundary formulation.
Best,
Christoph