There can be issues with the rendering order of elements in a Vue.js application when using the v-for directive. This is especially true if you are relying on the index for conditional rendering or animations.

Here's how to fix this issue:

1. Use a stable key: Ensure that each element rendered by v-for has a unique and stable key. The key should not change during re-rendering, unless it is guaranteed to be different. This will help Vue.js keep track of the elements in the correct order.

2. Use Keep Alive with Router: If you are using Vue Router for your application, make sure to use keep-alive component along with router-view. The keep-alive component will preserve the state of components while they are deactivated, which can help prevent issues with rendering order.

3. Sort Your Data: If you are sorting your data before passing it to the v-for, ensure that each item in the array has a unique key and that the sort function is stable (i.e., doesn't change the index of elements).

4. Use Computed Property or Watcher: You can use computed properties or watchers to generate a new list of data based on your original data, ensuring that the order is maintained. This will help you avoid modifying the original data and causing issues with rendering order.

5. Avoid Using Index as a Key: Instead of using the index as a key, consider generating a unique key for each element. This can be done by creating a unique identifier for each item in your data array, which can then be used as a key in v-for. This will ensure that Vue.js keeps track of the elements in the correct order.

Here's an example of using a computed property to generate a new list based on the original data:

<template>
  <ul>
    <li v-for="item in sortedItems" :key="item.id">{{ item.name }}</li>
  </ul>
</template>

<script>
export default {
  data() {
    return {
      items: [
        { id: 1, name: 'Item 1' },
        { id: 2, name: 'Item 2' },
        { id: 3, name: 'Item 3' }
      ]
    }
  },
  computed: {
    sortedItems() {
      return this.items.slice().sort((a, B) => A.name.localeCompare(B.name));
    }
  }
}
</script>