'Guest users cannot be record owners' error during deployment of test class to production

I have increased test coverage of a class in QA Sandbox and I am trying to deploy that test class to production. When I run the test class in QA Sandbox, there is no error. But when I am deploying it to production, I am getting an error 'Guest users cannot be record owners'.

Here is a screenshot of the error:

The class has nothing to do with communities. I am not able to understand why I am getting the error in production and not in QA Sandbox.

The version of QA Sandbox and Production is Summer 20. I read that there were some changes in Summer 20 release regarding guest users (Release Notes). In release notes, there is a section Automatically Assign Records Created by Guest Users to a Default Owner. Here is the link. I verified that this checkbox is checked in both QA and production.

I am not able to find a way to solve this error. I am not able to answer why I am getting the error when the class has nothing to do with communities. Also, why am I getting the error in production and not in QA Sandbox even though class has the same code? Please guide. Thank You!