Member access within misaligned address with linked-list

Question

So I'm working out the problem number 2 of leetcode (basically you got 2 numbers reversed in a list and need to sum them and return the answer in an inverted list too). However I keep getting this annoying error: "Runtime error: member access within misaligned address 0x000000000031 for type 'struct ListNode', which requires 8 byte alignment". I run it on my machine and it works fine, giving the expected results. My code:

/*Definition of the list:
struct ListNode {
         int val;
         struct ListNode* next;
    };*/

struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {
    struct ListNode* answer = malloc(sizeof(struct ListNode));
    answer->next = NULL;
    answer->val = 0;
    int auxInt = 0;
    struct ListNode* auxVar = answer;

    while(l1 != NULL || l2 != NULL) {
        if(!l1) {
            auxInt = answer->val;
            answer->val = (auxInt + l2->val) % 10;
            if(((l2->val + auxInt) / 10) != 0) {
                answer->next = malloc(sizeof(struct ListNode));
                answer->next->val = (l2->val + auxInt) /10;
            }
            l2 = l2->next;
        }
        else if(!l2) {
            auxInt = answer->val;
            answer->val = (auxInt + l1->val) % 10;
            if(((l1->val + auxInt) / 10) != 0) {
                answer->next = malloc(sizeof(struct ListNode));
                answer->next->val = (l1->val + auxInt) /10;
            }
            l1 = l1->next;
        } else {
            auxInt = answer->val;
            answer->val = (l1->val + l2->val + auxInt) % 10;
            if(((l1->val + l2->val + auxInt) / 10) != 0) {
                answer->next = malloc(sizeof(struct ListNode));
                answer->next->val = (l1->val + l2->val + auxInt) /10;
            }
            l1 = l1->next;
            l2 = l2->next;
        }
        if(l1 == NULL && l2 == NULL)
            break;
        else
        {
            if(!answer->next)
                answer->next = malloc(sizeof(struct ListNode));
            answer = answer->next;
            answer->next = NULL;
        }
    }
    return auxVar;
}

Any thoughts on what might be causing this problem? Thanks for your time.

Edit: here is a verifiable example with the numbers that result the crash:

#include <stdio.h>
#include <stdlib.h>

struct ListNode {
    int val;
    struct ListNode *next;
};

/*typedef struct InvertedList {
    int val;
    struct InvertedList *next;
    struct InvertedList *previous;
}Lista;*/

struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {
    struct ListNode* answer = malloc(sizeof(struct ListNode));
    answer->next = NULL;
    answer->val = 0;
    int auxInt = 0;
    struct ListNode* auxVar = answer;

    while(l1 != NULL || l2 != NULL) {
        if(!l1) {
            auxInt = answer->val;
            answer->val = (auxInt + l2->val) % 10;
            if(((l2->val + auxInt) / 10) != 0) {
                answer->next = malloc(sizeof(struct ListNode));
                answer->next->val = (l2->val + auxInt) /10;
            }
            l2 = l2->next;
        }
        else if(!l2) {
            auxInt = answer->val;
            answer->val = (auxInt + l1->val) % 10;
            if(((l1->val + auxInt) / 10) != 0) {
                answer->next = malloc(sizeof(struct ListNode));
                answer->next->val = (l1->val + auxInt) /10;
            }
            l1 = l1->next;
        } else {
            auxInt = answer->val;
            answer->val = (l1->val + l2->val + auxInt) % 10;
            if(((l1->val + l2->val + auxInt) / 10) != 0) {
                answer->next = malloc(sizeof(struct ListNode));
                answer->next->val = (l1->val + l2->val + auxInt) /10;
            }
            l1 = l1->next;
            l2 = l2->next;
        }
        if(l1 == NULL && l2 == NULL)
            break;
        else
        {
            if(!answer->next)
                answer->next = malloc(sizeof(struct ListNode));
            answer = answer->next;
        }
    }
    return auxVar;
}

void adicionaLista(struct ListNode* ptrLista, char *array, int size) {
    struct ListNode *auxNode = ptrLista;
    for(int i = 0; i < size; i++) {
        ptrLista->val = array[i];
        if(i + 1 != size) {
            ptrLista->next = malloc(sizeof(struct ListNode));
            ptrLista = ptrLista->next;
        }
    }
    ptrLista = auxNode;
    printf("\n");
}
void printAnswer(struct ListNode *ptrAnswer) {
    for(; ptrAnswer != NULL; ptrAnswer = ptrAnswer->next)
        printf("%d ", ptrAnswer->val);
}

int main()
{
    struct ListNode *l1 = malloc(sizeof(struct ListNode));
    struct ListNode *l2 = malloc(sizeof(struct ListNode));
    char lista[9] = {4,5,2,2,9,3,8,9,2};
    char lista2[9] = {0,7,6,1,6,5,0,6,7};
    adicionaLista(l1, lista, 9);
    adicionaLista(l2, lista2, 9);
    struct ListNode *answer = addTwoNumbers(l1, l2);
    printAnswer(answer);
    return 0;
} 

Answer 1

The main problem is that next in the last element isn't set to NULL.
Secondary problems are...

1. It is expected not to create an empty list, that is, a situation where useless nodes are created.
2. There are many duplications in the code. That makes it difficult to change the code.
3. printf("\n"); should not be included in additional functions of data. It should be used in output functions.

fixed and reduced code

#include <stdio.h>
#include <stdlib.h>

struct ListNode {
    int val;
    struct ListNode *next;
};

struct ListNode *addTwoNumbers(struct ListNode *l1, struct ListNode *l2) {
    struct ListNode anchor  = { .next = NULL }, *curr = &anchor;
    int carry = 0;
    while(l1 != NULL || l2 != NULL || carry) {
        int val1 = 0, val2 = 0;
        if(l1) {
            val1 = l1->val;
            l1 = l1->next;
        }
        if(l2) {
            val2 = l2->val;
            l2 = l2->next;
        }
        int answer = val1 + val2 + carry;
        carry = answer > 9;//val1 and val2 are one digit.
        curr = curr->next = malloc(sizeof(struct ListNode));
        curr->val = answer % 10;
        curr->next = NULL;
    }
    return anchor.next;
}

struct ListNode *makeListFromChars(const char *array, int size) {
    struct ListNode anchor  = { .next = NULL }, *curr = &anchor;

    for(int i = 0; i < size; i++) {
        curr = curr->next = malloc(sizeof(struct ListNode));//Creating lists and adding data is a separate function.
        curr->val = array[i];
        curr->next = NULL;
    }
    return anchor.next;
}

void printList(struct ListNode *p) {
    for(; p; p = p->next)
        printf("%d ", p->val);
    printf("\n");
}

int main(void){
    char lista1[9] = {4,5,2,2,9,3,8,9,2};
    char lista2[9] = {0,7,6,1,6,5,0,6,7};
    struct ListNode *l1 = makeListFromChars(lista1, 9);
    struct ListNode *l2 = makeListFromChars(lista2, 9);

    printList(l1);
    printList(l2);

    struct ListNode *answer = addTwoNumbers(l1, l2);
    printList(answer);
    //freeList(l1);freeList(l2);freeList(answer);
    return 0;
}