401 unauthorized response from enterprise connected workspace with Atlassian Guard enabled

ACSB 2.3.6
SB 2.7.17

We have a specific enterprise customer workspace that is failing to make the API calls from our jira-connect addon. In particular we see this behavior on the /rest/api/2/project/search endpoint, and others. The endpoint api calls we make to this workspace are all failing with 401 unauthorized, and we are served this unconventional html error page:

<p>Encountered a <code> 401 - Unauthorized </code> error while loading this page.</p>
<p><a href="/secure/MyJiraHome.jspa">Go to Jira home</a></p>

There are a lot of details in the html error response we receive to this json api call, but nothing specific about what has failed with the request. The addon is able to install into the workspace just fine; subsequent API calls then fail.

We have many other established jira addon workspaces are connected and we can make api calls on behalf of. This customer has two paid enterprise Atlassian workspaces that both cannot connect with our addon for similar reasons. The customers is also getting established with Atlassian Guard, although they do not have a data security policy setup.

Does this html error response look familiar for this endpoint response? Is there specific behavior from Atlassian Guard that would deny API calls from our jira-connect addon?