Right yeah. It's a really weird thing I'm not understanding. If it's any help: I've been trying to solve this inconsistency issue for a while now and a couple weeks ago I thought I had found the problem. In the geometry, there was just 1 pressire far-field being used to describe two orthogonal faces of the enclosure (inlet and open air) and when I changed this to be 2 separate pressure far-fields for each face, the divergence didn't occur in the HPC system case as well. (This was just in this specific case - though it made me think I had solved the problem)
But this wasn't the issue for everything, since I do this (split up far-field procedure) with new case files of slightly different geometry and the divergence returns again, just for the HPC solution.