"403 Could not find app auth type" API error with JIRA Issues

We’re encountering an error we’ve not seen before when retrieving certain Issues and Issue-related resources for some of our Connect app users with the JIRA REST API.

403: Could not find app auth type

The specific endpoints we’re hitting are GET calls for these resources: Issue, Issue Remote Link, Issue Comment, Issue Vote, Issue Watcher, Issue Worklog, Issue Link.

We’re only getting the error for some of each resource, not all. For example, we were successfully able to make the GET Issue call for 613 out of 631 of one user’s Issues.

Anyone able to provide any insight into the meaning of this error? The error message leads us to suspect the user might have another third-party app connected to the ‘problem’ issues.