Hello Bruno,
a) Its evolution is stopped with Nans around 8.6M. Nans appear to come from the BSSN fields, but still needs further investigation.
Hmm I could evolve the qc0 example in McLachlan. Maybe there are differences in the parameter file that make the error "obvious".
c) When CarpetReduce::weight is output, its values seem strange to me. Most of the domain has 1/2 set. A few points close to the boundary 1/4 and the boundaries 0 (physical and ghost). No mask out values inside AH is shown, ie they still are set to 1/2. These values seem to make more sense to AMR restriction operations.
Are you maybe looking at the z=0 plane? That plane has a weight of 1/2 since only half of the volume of each cell is used when eg. computing the simulation volume. I have never used CarpetMask myself (but have written a similar thorn of my own... would have paid to look into Carpet first I guess :-) )
Yours Roland