Comment (by Roland Haas):

Ok, in some sense this is actually good news (at least it’s not obviously a race condition). Being paranoid, did you check in RunScript that it does indeed set OMP_NUM_THREADS=8 (Carpet also prints out the number of threads used at the top of the out file, in a line INFO (Carpet): There are 24 threads per process).

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2670/refinement-prolongation-all-points-must