This is so weird, I run with

mpirun -np 4 smoothMesh -parallel

, decomposeParDict says

numberOfSubDomains 4

, it runs fine till the end but and at the very end of run it says

[0] --> FOAM FATAL ERROR: 
[0] "/path/to/smoothMesh/run_tests/testcase4/system/decomposeParDict" specifies 4 processors but job was started with 3 processors.

When I run with

mpirun -np 2

with

numberOfSubDomains 2

it runs happily till the end and says

number of processor directories = 2 is not equal to the number of processors = 3

When I run with three processors, it does not complain anything. 🤷 What is going on?