Jinja2 Repeats Table Rows When Reloading Page - flask

Question

I have a 'dashboard' page that comes up after a user selects a project that they'd like to inspect the details on. Some of these details are displayed in a table format. Below is a portion of the Jinja2 template:
`
{% if release_container.nreleases > 0 %}
<table class="table table-bordered">
<thead>
<tr>
<th scope="col">Name</th>
<th scope="col">Date Created</th>
<th scope="col">Status</th>
<th scope="col">Date Released</th>
</tr>
</thead>
<tbody>
{% for rh in release_container.release_history %}
<tr>
<td>{{rh.name}}</td>
<td>{{rh.creation_date}}</td>
<td>{{rh.status}}</td>
<td>{{rh.release_date}}</td>
</tr>
{% endfor %}
</tbody>
</table><!--ends table-->
{% endif %}
`
If I reload the page, or click on a link and then come back to the page, the same data will get appended. As an example, here's the HTML from a 'fresh' load, which is what I should look like after a reload as well:
`
<tbody>
<tr>
<td>v0.1</td>
<td>2022-11-10</td>
<td>False</td>
<td>2022-11-10</td>
</tr>
<tr>
<td>v0.2</td>
<td>2022-11-17</td>
<td>False</td>
<td>2022-11-17</td>
</tr>
</tbody>
`
But this is what it looks like when the page is reloaded:
`
<tbody>
<tr>
<td>v0.1</td>
<td>2022-11-10</td>
<td>False</td>
<td>2022-11-10</td>
</tr>
<tr>
<td>v0.2</td>
<td>2022-11-17</td>
<td>False</td>
<td>2022-11-17</td>
</tr>
<tr>
<td>v0.1</td>
<td>2022-11-10</td>
<td>False</td>
<td>2022-11-10</td>
</tr>
<tr>
<td>v0.2</td>
<td>2022-11-17</td>
<td>False</td>
<td>2022-11-17</td>
</tr>
</tbody>
`
What do I need to do in order to stop this from happening? I presume this is some kind of cache setting?
Thank you in advance for any assistance.
I've debugged the code by printing out the lengths of the various arrays to see if they change on reload, thinking that the data was being appended to the array, but the length remains '2', even though 4 different entries are rendered.
EDIT
A commenter asked to see the view code. At this point in time, it's a huge function that generates the containers that get passed to the template (which is just one template amongst half a dozen that gets passed), and I'll be refactoring that code shortly into more palatable bites, but hopefully the snippet below provides more context:
for release in releases:
rhistory_container = ProjectDashboardReleaseHistoryContainer()
rhistory_container.rid = release.id
rhistory_container.name = release.name
rhistory_container.creation_date = release.created
rhistory_container.status = release.is_active
release_container.release_history.append(rhistory_container)
"""
"""
return render_template('project_home.html',parent_container=parent_container,release_container=release_container,testing_container=testing_container,reqs_container=reqs_container,sw_container=sw_container,hw_container=hw_container)