Metis returns proxy-violating partitions
One other fun aspect of @rttw52's runs was that we hit a bug related to the partitions metis generates. At the moment the code cannot handle more than 64 proxies for a given MPI rank. There is a fail-safe in engine_makeproxies() to prevent more problems down the line.
However, there is nothing in the code preventing metis from generating a partition which would violate that constraint. I don't know whether that is something that can be done but it could be useful to investigate whether we can demand that from metis. It does not seem to happen in regular runs where the domains are nice and compact but since it can in principle happen we should think about it.
Of course, we could increase the number of proxies somehow or use a clever algorithm in makeproxies to reduce the number of unnecessary proxies created but that is only a workaround.