Removing a child element may cause the current scroll position of the parent to become invalid. This was reported and partially fixed in #3210.

Looking at the original reproducer, there's another way to remove obj3 that still exhibits the bug:

    if(code == LV_EVENT_CLICKED) {
        lv_obj_set_parent(obj0, obj2);
        lv_obj_set_parent(obj3, lv_scr_act()); // instead of lv_obj_del_async(obj3);
    }

To fix both, add a general mechanism to call lv_obj_readjust_scroll() after revalidating the layout. This also fixes (or at least significantly improves) the performance issue in #4908.