Hi olaf@xso,
For some reason it is necessary to include a wrapper around the router-view in order to work. This should fix the problem:

<template>
  <div>
    <smart-splitter>
      <smart-splitter-item size="180">
        <router-link to="/">Home</router-link><br />
        <router-link to="/about">About</router-link>
      </smart-splitter-item>
      <smart-splitter-item>
        <div>
          <router-view :key="$route.path" />
        </div>
      </smart-splitter-item>
    </smart-splitter>
  </div>
</template>

Best Regards,
Christopher
Smart HTML Elements Team
https://www.htmlelements.com