In every instance I have come across this problem myself, it was due to the account I was using lacking either a role or a specific permission to access/read a group, so a user error on my part. Reviewing or rubber-ducking your access permissions is probably a good start.
Maybe create a new useraccount, grant the necessary permissions/roles and check if you can access the ticket with that account? If you can, compare permissions/roles between that account and your own.
I found out that the issue is that the group the ticket belongs to has been deactivated. It would be great if Zammad could give a better error message than “No access”.
Zammad is constantly evolving and changing.
It’s kinda difficult to flex that “be better” when using a Zammad 4.1 which is terribly outdated (5.2.1 by now) without re-visitting if the message has changed.
If you think something doesn’t go the way it should and should be improved, you’re always very welcome to create a feature request post in this section: Feature requests - Zammad - Community