Not sure about how to interpret the analysis results of gprof

Question

So I've used gprof to analyze my C++ code. The top three that make my code lag are as follows:

  %   cumulative   self                  self     total           
 time   seconds   seconds    calls      ms/call  ms/call     name    
 66.00    521.93   521.93 12674073276     0.00     0.00      std::_List_const_iterator<std::unique_ptr<Msg, std::default_delete<Msg> > >::operator++()
 13.63    629.70   107.77                                    _mcount_private
  9.47    704.63    74.93                                    __fentry__

I guess the second and the third are from gprof itself. But what does std::_List_const_iterator<std::unique_ptr<Msg, std::default_delete<Msg> > >::operator++() really mean? And why this causes slowness?

For reference, I have two important member variables:

std::list<std::unique_ptr<struct A> > queue_1;
std::vector<std::deque<std::list<std::unique_ptr<struct A> >::iterator > > queue_2;

So queue_2 is to store iterators to queue_1. There is supposed to be frequent push_back() and element deletions applied to the two queues.