Feature request

Is your feature request related to a problem? Please describe.
We recently had multiple bugs when running with 5 processes.
These are not caught in the CI since it only tests with 4 processes.

Describe the solution or feature you'd like
Change some test to check with different MPI numbers.
5 should be present at least, but we should also include other counts ideally.

Describe alternatives you've considered
Not testing will result into bugs.

Estimated priority
Which of these is most applicable (remove the others):

"Priority: medium" Should be solved within half a year

Additional context
This is related to Continuous benchmarking and may be resolved there as well. Ping @spenke91