After importing some published articles from one instance to another, the 'Checkout' button is missing in the target instance.
The issue is impacting all users and prevents them from creating new article versions.
The imported articles had versioning enabled however the related records from the kb_version table were not imported.
This can be reproduced by exporting the last published version of an article (i.e.: 'KB0010027 v2.0') to another instance with article versioning support.
After importing the article in the target instance, once you open it, the checkout button will be missing and the article number may have a 'v' in the end with no numbers (i.e.: 'KB0010027 v').
You can also export and import other kb_knowledge table records related to the same article (i.e.: 'KB0010027 v1.0').
By doing that you will be able to see both article records in the kb_knowledge table, however the checkout button will still be missing.
In order to resolve that, you need to also export the kb_version table record related to the latest article version (in this example the version 2.0).
Once the kb_version record is imported into the target instance, the checkout button will get visible in the article.
After that you will be able to checkout the article and create a new version.
As expected, as per this example, once the article is checked out the version 2.01 is created then once the article is saved the 2.02 version (awaiting approval) and finally the version 3.0 when the article is published.
So ideally, to properly restore the articles you need to export and import all versions of the same article in the kb_knowledge table and all related version records on the kb_version table.
That way we can ensure there is no random issues that may occur in the future.