Steps to replicate :

1. Create Jira project
2. Create an issue in that project
3. Delete the issue
4. Reopen the page of that issue by giving the issue number directly in the URL

Existing text when issue is missing or the user does not have access

An error is shown that emphasizes the following text :
You don't have access to this issue

The description then goes on to say that the issue might not exists as described in the screenshot below :

Suggested text

The title of the error message could be the following :
You don't have access to this issue or the issue might not exist.

This is because it would be easier for the user to read if the text is emphasized in the title