Hello to all who visit this thread
Both I and many other people have been using the new Service Accounts configured with OAuth 2.0 scopes, both Classic and Granular, for a many months now and have had not encountered any of the problems mentioned in the original poster’s question. The results returned from any of the JQL based endpoints, such as the Search for Issues using JQL endpoint, are exactly as expected for the scopes applied to the account, and the same is true for any other API endpoints and their scopes.
I suggest that you might be just doing something basically wrong, so double-check your method with your API test tool and have a work colleague peer review your code.
If nobody in your team can uncover the mistake in your code or method, then post a new question with a FULL description of the entire problem, as per the How to ask a good question thread. If a genuine problem with the functionality of the new Service Account’s use of OAuth 2.0 credentials is found, then a proper bug needs to be logged with the dev help desk; simply posting “me too” in someone else’s unanswered thread isn’t particularly informative or constructive.
Thank you.