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it is possible that there was a problem reading the restart files. Check in the listings of all processes if you find a message like:
oe-00000-...: forrtl: severe (24): end-of-file during read, unit 999, file .../gem_restart
If you find such a line you need to restart the simulation from the previous restart file.
If you find no error message at all there might have been a problem with the machine machine problem and the MPI processes could not all get started or that your restart files are corrupted but you can't see it. If this happens for the first time for a given month you can just restart the simulation. But if this happens more than once I would restart the simulation from the previous monthrestart file, assuming there is a problem with the restart files.
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