We have found the issue. In our site, there is a custom hierarchical taxonomy and in which, we have more than 10000 terms ( parent-child) in it. While adding ‘relationship’ field under a field group, ACF is trying to query all those terms for its filter options. Due to more no of terms, it took long time to load that filter options. That query become very expensive due to that parent child hierarchical terms.
We hope it might help others who has similar issue with ACF relationship field and more no of parent-child terms.
