I am on Jira Cloud and created a version. I added an issue to that version while in the backlog and the version showed up in the row. The issue also displays the associated version in "Fix Versions" field.
After adding it to the version, I can click on the Version in the backlog and it will filter correctly.
If I refresh the page at this point and click on the new version again, it is no longer there. The issue still has the version associated with it, but it does not show up in the filtered backlog. The issue does not display under the Releases page either.
The only possible resolution I could find was to re-index my instance manually but it appears that option has been deprecated for Cloud, so I am not sure what to do now.