It seems that setting
[backend-openmp]
gimmik-max-nnz = 8192
as suggested in https://pyfr.discourse.group/t/keyerror-on-3d-case-running-with-wsl-ubuntu-openmp/404/9, made the simulation ongoing.
What I really cannot understand is the reason: why the cuda-backend would not require to enlarge the number of non-zero elements in a constant matrix for Gimmik?
Any hints would be greatly appreciated!
Best,
Federico Cipolletta.