Here's how I resolved the markup errors after the latest Google update, as mentioned in "Implemented - Markup improvements for Google":
REPLACE WITH
Schema Markup Validator
validator.schema.org

- Edited the post_macros template.
- Located the relevant paragraph section.
- Made the necessary adjustments.
HTML:
<xf:if is="$includeMicrodata">
<meta itemprop="parentItem" itemscope itemid="{{ link('canonical:threads', $thread) }}" />
</xf:if>
REPLACE WITH
HTML:
<xf:if is="$includeMicrodata">
<meta itemprop="parentItem" itemscope itemid="{{ link('canonical:threads', $thread) }}" />
<div itemprop="author" itemscope itemtype="https://schema.org/Person">
<meta itemprop="name" content="{{ $post.User.username ?: $post.username }}" />
<meta itemprop="url" content="{{ link('canonical:members', $post.User) }}" />
</div>
<meta itemprop="text" content="{{ $post.message }}" />
<meta itemprop="url" content="{{ link('canonical:posts', $post) }}" />
<meta itemprop="name" content="Post by {{ $post.User.username ?: $post.username }}" />
</xf:if>
validator.schema.org
