Getting invalid pointer error for openmp parallel code

Question

I am trying to compute the number of triangles for each edge in an OpenMP parallel code. Following is the code snippet where I am doing it. While running with multiple OpenMP threads, once in a while I am getting the following error

munmap_chunk(): invalid pointer: 0x00000100002500e0 ***

However, when I am running in a single thread, I am not getting any errors. Any suggestions on what's wrong with the code?

///graph is declared as follows map<int, std::map<int, Edge>> graph, where the first key is the vertex u and the keys of the second map are all the adjacent vertices
    
    int smax = 0;
    
    #pragma omp parallel for reduction(max:smax)
    for(int i = 0; i < vertexIds.size(); i++)       //vertexIds is a vector of all the vertices
    {
        int u = vertexIds[i];
        for(map<int, Edge>::iterator it2 = graph[u].begin(); it2 != graph[u].end(); it2++)
        {
            int v = it2->first;
            Edge edge = it2->second;
            if(u < v)
            {               
                if(tricount.find(edge) == tricount.end()) //tricount is a map for storing number of triangles for each edge
                {
                
                    int s = 0;
                    
                    for(map<int, Edge>::iterator it3 = graph[u].begin(); it3 != graph[u].end(); it3++)
                    {
                        int w = it3->first;
                        
                        if(v != w)
                        {
                            
                            if(graph[v].find(w) != graph[v].end())
                            {
                                s++;
                            }
                        }
                    }

                    if (s > smax)
                    {
                        smax = s;
                    }

                    tricount.insert(make_pair(edge, s));
                }
            }
        }           
    }
    return smax;