I'll note down the mysteries here to report to Maxime later:
Initially, it failed only when compiled in Fortran
I tried to remove the SumWaBal argument from GlobalZero (in global.f90) and use directly the setters in the procedure -> result: it failed also when compiled in Fortran
I re-introduced the PreviousSum argument in ResetPreviousSum (run.f90) and it worked
So the PreviousSum_temp problem has been fixed, I don't understand why or how but it works... Tests (compiled in Pascal and Fortran) are OK