Conversion from jira leverages the HTML output which is something like

<p>Internal error appears:</p>

<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
<pre class="code-java">
ERROR GENERAL - Unhandled exception - <span class="code-keyword">null</span>
java.lang.StackOverflowError: <span class="code-keyword">null</span>

This HTML means nothing to Tuleap so it's only rendred as a <pre> block.

The conversion process should instead produce Tuleap Markdown with appropriate ```LANG block.

Internal error appears:

ERROR GENERAL - Unhandled exception -  null
java.lang.StackOverflowError: null