The returned value from G4ProcessManager::GetProcessListLength() happened to be
2x bigger than G4ProcessManager::GetProcessList()->length() for the particle
Cr51[0.0] (coming from PiMinusAbsorptionAtRest process).
Possible reason for that can be (?) the copy constructor of G4ProcessManager:
G4ProcessManager::G4ProcessManager(G4ProcessManager &right)
               :duringTracking(false)
{
  // .. skipped
   numberOfProcesses  = right.numberOfProcesses;
  // ...skipped

   for (G4int idx=0; idx < right.numberOfProcesses; idx++) {
     // copy contents in theProcessList
     // ... skipped
       numberOfProcesses +=1;
   }
   // ...
}