How to access a 2d array inside a struct using only pointers

Question

Trying to understand pointers as a beginner in C- I've got this struct:

    typedef struct {
        int size;           // dimension of array
        int **arr; // pointer to heap allocated array
    } someStruct;

So I use malloc to generate this struct, and an array, and initialize all the values to zero-

someStruct *m = (someStruct*)malloc(sizeof(someStruct));
m->size = n;
m->arr = (int**)malloc(n * sizeof(int));
// initialize array
for (int i = 0; i < n; i++) {
    *(m->arr + i) = (int*)malloc(n * sizeof(int));
    // set value to 0
    for (int j = 0; j < n; j++) {
        *(*(m->arr + i) + j) = 0;
    }
}

After this I basically continue to access the array in later stages using the same kind of pointer logic-

for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
        int num =  *(*(m->arr + i) + j);
        printf("num: %d\n", num);
    }
}

Here's the problem- when I try to use this method of access, I'm clearly not getting the right answer- my print output look like this:

num: -2043774080
num: 22031
num: 0
num: 0
...
num: 0
num: 0

Here's the really weird part- this seeming bug of the 'weird' random numbers only comes when I'm creating and accessing an array of size 5-

I've come to believe that the whole

*(*(m->arr + i) + j)

method of access must be wrong- any help on this would be really useful. Thanks in advance, I apologize if this was already answered, my searching was unable to find it.