It is possible to output invalid markup when truncated since summary and body are HTML.

description is text so not an issue.

not sure i understand. description is in fact summary.
introtext is summary and body is fulltext

Here is from the Joomla! Testing article where the bulleted list is missing the beginning markup <ul>.

			<p class="result-text">
			of rendering--items not aligned correctly, missing or wrong images, pages that just don't look right.</li>
<li>Unexpected behavior--anything that is working differently than it did in 2.5.</li>
</ul>
<p>Report problems</p>
<p>If you find a problem</p>...		</p>
				<div class="small result-url">
			http://localhost/joomla-cms-staging/index.php		</div>
	</li>
	</ul>
<br id="highlighter-end" />

Add var_dump($this->result); exit; above // Make sure we highlight term both in introtext and fulltext to see the values for summary, body, and description. Only description is text where the summary and body are HTML.

@Quy
Understood now. Thanks.
Corrected patch.
To test, first make sure you added a readmore in that same article.
Then add a var_dump($full_description); exit; before // Find the position of the search term
Search a term which is placed after the readmore.
we now get text only.

In the screenshot below the first article has a readmore, the second one not.

I have tested this item ✅ successfully on 770422e

@Ooops-404
please test

I have tested this item ✅ successfully on 770422e

Ready to Commit after two successful tests.