PyBaMM Version

develop

Python Version

3.10, 3.12

Describe the bug

There is an intermittent failure on CI resulting from #5112

See:
https://github.com/pybamm-team/PyBaMM/actions/runs/16673618028/job/47195320616?pr=5129
https://github.com/pybamm-team/PyBaMM/actions/runs/16605096852/job/46974781286

There are more if you look.

I think this happens on line 101 of the new SciKit FEM 3D code.

@Rishab87 Can you please take a look at this? It looks like the inverse mass matrix can be a scalar in some non-deterministic case, which causes this? This seems strange to me

Tagging @rtimms @kratman

Steps to Reproduce

This failure appears to be non-deterministic 😬

Relevant log output

see the linked PR's