what you are seeing is based on a change which Community was informed about this week by this post:
An Atlassian Team member wrote as for concerns as the very same you are experiencing right now:
We are aware of this issue that is impacting a very small number of instances with complex configurations and are working on a fix. In the meantime, if you would like to switch back to tabs on the right hand side of the issue view please contact support and they will be happy to switch you back.
So I'd suggest to open a request with Atlassian support and ask for a switch back to old display behaviour.
Please let us know here in Community if there are some other questions.
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