Gaussian-4 (G4) theory calculations in Gaussian 16 Rev. B.01 can produce erratic results. A workaround is to use Gaussian 16 Rev. A.03:
module load gaussian/g16a03
Gaussian 16 Rev. A.03 has been made the default module on all clusters. A typical symtom is energy blow up in step 8 resulting in an unusually large, erroneous HF/GFHFB2 energy and consequently an incorrect G4 total energy.