Why ios::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL); causing Runtime error(SIGSEGV)

Question

I was solving the Substring problem using KMP Algorithm (Problem link). After getting runtime error (SIG_SEGV) several times, I just removed the following part:

ios::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
    

and the solution was accepted. What was the issue? I think the implementation here isn't important, but if anyone is interested I've attached the full code below: Details implementation: Before and After