Using HadronElasticPhysicsHP does not include elastic process for He3, looking onto G4HadronElasticPhysics.cc in fact shows that in line 163 it is missing (among other light nuclei). Adding it into the "if()" statement seems to work.
Hello, thanks for reporting this. You are right: He3 was missed in Geant4. This has been fixed in the coming patch G4 10.2.p01, expected this week, and will also be fixed in the future patch G4 10.1.p04.