Comment (by Miren Radia):

The problem is likely that the grid is too small for the given number of GPUs.

I’m not sure about this. I only ran on a single GPU (initially I started on 8 but realised that I could reproduce on just 1) and also started with a more production-sized parameter file with the following grid configuration that reproduces the same problem:

$nlevels = 10

CarpetX::xmin = -512.0
CarpetX::ymin = -512.0
CarpetX::zmin = -512.0
CarpetX::xmax = 512.0
CarpetX::ymax = 512.0
CarpetX::zmax = 512.0

CarpetX::ncells_x = 128
CarpetX::ncells_y = 128
CarpetX::--

Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2890/carpetx-crash-failed-assertion-in-z4c_rhs