vtable C++ error after implementing pure virtual method

I have a pure virtual function defined in a class as below:

   template <typename T>
   class PositioningMethod {

   public:
       virtual ApproximatePosition *getPosition(std::list<T*> &observedRadioSignals) = 0;
   };

and implementing it in ParticleFilter as below:

     class ParticleFilter:public PositioningMethod<T> //implements PostioingMethod
{

        public:
            virtual ApproximatePosition *getPosition(std::list<T*> &observedRadioSignals) {
           /*Some code and return*/
        return ApproximatePosition::from(xxxx, xxxx, xxxx());

        }
        }

but getting below errors:

    "ParticleFilter<KnownBluetoothBeacon<CartesianLocation>, RadioProximity<BluetoothBeacon>
   >::getPosition(std::__1::list<RadioProximity<BluetoothBeacon>*, std::__1::allocator<RadioProximity<BluetoothBeacon>*> >&)",    referenced from:
             vtable for RadioProximityParticleFilter in libSIS_MOBILITY_J2C.a(RadioProximityParticleFilter.o)
         "ParticleFilter<KnownBluetoothBeacon<CartesianLocation>, RadioProximity<BluetoothBeacon>
   >::ParticleFilter(std::__1::list<KnownBluetoothBeacon<CartesianLocation>,    std::__1::allocator<KnownBluetoothBeacon<CartesianLocation> > >&,    double)", referenced from:
             RadioProximityParticleFilter::RadioProximityParticleFilter(std::__1::list<KnownBluetoothBeacon<CartesianLocation>,    std::__1::allocator<KnownBluetoothBeacon<CartesianLocation> > >&,    double) in lib.a(RadioProximityParticleFilter.o)
       ld: symbol(s) not found for architecture arm64

I know vtable error generally occurs on non-implementing pure virtual functions, but in my case it is same. Any idea where I may be wrong?