When you face an issue where Vue.js scoped slots are not rendering as expected, it usually happens due to either a misunderstanding or misuse of the feature. Here are some steps to debug and fix this:

1. Check Your Slot Syntax: Ensure that you have the correct syntax for defining your scoped slot in both parent and child components. The basic syntax is as follows:

<!-- Child Component -->
<template v-slot:yourSlotName="props">
  <div>{{ props.childData }}</div>
</template>

<!-- Parent Component -->
<ChildComponent>
  <template #yourSlotName="{ childData }">
    <div>{{ childData }}</div>
  </template>
</ChildComponent>

2. Verify Props: Make sure that the props being passed into the scoped slot are correctly named and accessible within your child component.
3. Use Props Alias: If you want to change the prop names in the parent, use an alias by defining it in the template like this:

<!-- Child Component -->
<template v-slot:yourSlotName="{ dataFromParent }">
  <div>{{ dataFromParent }}</div>
</template>

<!-- Parent Component -->
<ChildComponent>
  <template #yourSlotName="{ childData }">
    <div>{{ childData }}</div>
  </template>
</ChildComponent>

4. Check Template Nesting: Ensure that your scoped slot is not nested inside other elements (like divs, spans) in the parent component. This could cause it not to render properly. Consider using a wrapper div around your slots if they are nested.

5. Use v-slot Directive: In some cases, you might use slot-scope instead of v-slot. Vue uses v-slot now and is recommended for better clarity in templates. So, switch to using v-slot:

<!-- Child Component -->
<template slot="yourSlotName" slot-scope="props">
  <div>{{ props.childData }}</div>
</template>

<!-- Parent Component -->
<ChildComponent>
  <template #yourSlotName="{ childData }">
    <div>{{ childData }}</div>
  </template>
</ChildComponent>

6. Check Vue Version: Make sure you're using Vue 2.6 or higher to benefit from scoped slots feature.

By following these steps, you should be able to resolve the issue and make your scoped slots work as expected.