On G4LossTableBuilder.cc line 97, non-master threads attempt to unlock a mutex that was never locked, which is undefined behavior and causes this type of build to crash.

The Geant4 version tested was 10.6.1, with Visual Studio 16.4.5.

The affected code looks like this:

G4LossTableBuilder::G4LossTableBuilder(G4bool master) : isMaster(master) 
{
  theParameters = G4EmParameters::Instance();
  splineFlag = true;
  isInitialized = false;
  if(isMaster || !theFlag) {
#ifdef G4MULTITHREADED
    G4MUTEXLOCK(&ltbMutex);
    if(isMaster || !theFlag) {
#endif
      isMaster = true;
      theDensityFactor = new std::vector<G4double>;
      theDensityIdx = new std::vector<G4int>;
      theFlag = new std::vector<G4bool>;
    } else {
      isMaster = false; <--- This line is never hit in multithreaded builds
    }
#ifdef G4MULTITHREADED
  }
  G4MUTEXUNLOCK(&ltbMutex); <---- CRASH
#endif
}

I am not quite sure what is supposed to happen, but if G4MULTITHREADED is defined the code can be simplified to this:

G4LossTableBuilder::G4LossTableBuilder(G4bool master) : isMaster(master) 
{
  theParameters = G4EmParameters::Instance();
  splineFlag = true;
  isInitialized = false;
  if(isMaster || !theFlag) {
    G4MUTEXLOCK(&ltbMutex);
    isMaster = true;
    theDensityFactor = new std::vector<G4double>;
    theDensityIdx = new std::vector<G4int>;
    theFlag = new std::vector<G4bool>;
  }
  G4MUTEXUNLOCK(&ltbMutex);
}

So if isMaster is false, this will result in undefined behavior. Also, note that the line "isMaster = false" is never hit for multithreaded builds.