Source: dolfin Followup-For: Bug #980751 Hard to say what went wrong here, to be honest. As far as I can tell dolfin is innocent in any case. The problem was triggered in slepc and fixed by rebuilding slepc. On the face of it the problem is in the dependency relationship between slepc and openmpi.
There were a lot of updates to the openmpi suite (including pmix and ucx) in the past month. The openmpi library transition was already declared to libopenmpi3 (>= 4.1.0). It must be some subtlety in the handling of MPIU_SUM in openmpi 4.1.0, though it doesn't make sense that pmix or ucx would affect that. In short, buggered if I know. https://youtu.be/BmRUJGRwkj0?t=111
