Energy units for ions are often inconsistent in the code. For example, the dump of the FTF model says it's valid from 2 GeV to 100 TeV:

                           Hadronic Processes for GenericIon

  Process: ionInelastic
        Model:  Binary Light Ion Cascade: 0 eV  ---> 4 GeV
        Model:                      FTFP: 2 GeV ---> 100 TeV

However, I believe these figures are energy per nucleon rather than energy, so the units should be GeV/n and TeV/n. Indeed, when generating He4 projectiles with the gun generator setting the energy at 396 TeV there is no problem, while 401 TeV leads to a crash. So the energy figure in the model dump is E/n but the reported unit is E, while energy in the gun settings is total energy (which is fine, since units are GeV, TeV etc.).

This leads often to confusion. Units should be consistent with the reported figures and documentation should clearly state if a certain parameter is considered as energy or as energy per nucleon (for example, the argument of 	G4HadronicInteraction::SetMinEnergy).