Indexing error in C++ stl map when performing erase operation while iterating

Question

Below is my code for LEETCODE PROBLEM https://leetcode.com/problems/where-will-the-ball-fall/solutions/ :

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My approach is to create a map to store the initial positions of each ball in each respective column. Then I check whether the ball can go down the matrix by checking with the appropriate neighbor. If the ball can't go down I delete it from the map and in the end print the result for which the entries are present in the map, else -1.

The code's logic is working perfectly for all the test cases but on a later test case(input as [[-1,1,-1,-1,-1,-1,-1,-1,1,-1,-1,-1,-1,1,1,-1,-1,-1,1,1,1,-1,-1,1,1,-1,-1,1,-1,-1,-1,-1,-1,-1,-1,-1,-1,1,-1,1,-1,-1,-1,-1,-1,-1,-1,1,-1,-1,1,-1,1,-1,-1,1,1,-1,1,-1,-1,-1,-1,1,1,1,1,1,1,-1,1,1,1,-1,1,1,1,-1,-1,-1,1,-1,1,-1,-1,1,1,-1,-1,1,-1,1,-1,1,1,1,-1,-1,-1,-1]] from the server). The code stops working after key=14. What happens is it firsts find appropriate result for key=13, then deletes key=14 as it does not go down. But instead of going to next key which is 15 it goes back to 13 and terminates. NOTE: The problem is not that it terminates, but it goes back to 13 instead of 15. Please help me! Thanks in advance...

class Solution {
public:
    void display_map(map<int, pair<int, int>> m){
        for(auto i = m.begin(); i != m.end(); i++){
            cout << i->first << " " << i->second.first << " " << i->second.second << endl;
        }
    }

    bool check_neigh(int state, vector<vector<int>> grid, int i, int j){
        int new_i, new_j = j + state;

        if(new_j < 0 || new_j == grid[i].size()) return false;

        if(state == grid[i][new_j]) return true;

        return false;

    }

    vector<int> findBall(vector<vector<int>>& grid) {
        vector<int> answer;
        map<int, pair<int, int>> Balls;
        
        for(int i=0; i < grid[0].size(); i++){
            Balls[i].first = 0;
            Balls[i].second = i;
        }

        // display_map(Balls);
        // cout << endl;

        bool flag1 = true;
        bool flag2 = true;
        int level = 0;

        while(Balls.size() != 0 && flag1){
            cout << "--------------------Next Cycle--------------------\n";
            auto i = Balls.begin();
            
            for(; i != Balls.end(); i++){
                cout << "Beginning: " << Balls.begin()->first << endl;
                int key = i->first;
                int m = i->second.first;
                int n = i->second.second;

                // if(m > level) continue;

                cout << "key: "<<i->first <<  " m: " << m << " n: " << n << endl;

                if(m >= grid.size()){
                    flag2 = false;
                    break;
                }

                int state = grid[m][n];

                bool stat = check_neigh(state, grid, m, n);

                if(stat == true){
                    i->second.first += 1;
                    i->second.second += state;
                    
                    cout << "New key: "<<i->first <<  " m: " << i->second.first << " n: " << i->second.second << endl;
                }
                else if(stat == false){
                    cout << "Deleted key: "<< i->first << endl;
                    Balls.erase(i);
                }
                // level++;
                display_map(Balls);
            }

            
            // for(auto i = Balls.begin(); i != Balls.end(); i++){
            //     if(i->second.first == level){
            //         Balls.erase(i);
            //     }
            // }
            // level++;

            display_map(Balls);


            if(flag2 == false){
                flag1 = false;
            }
        }


        for(int i = 0; i < grid[0].size(); i++){
            if(Balls.find(i) != Balls.end()){
                answer.push_back(Balls[i].second);
            }
            else{
                answer.push_back(-1);
            }
        }



        return answer;
    }
};