Important: If you are a Zammad Support or hosted customer and experience a technical issue, please refer to: support@zammad.com using your zammad-hostname / or company contract.
Used Zammad version: 2.9.x
Used Zammad installation source: package
Operating system: CentOS 7.6.1810
Browser + version: Chrome 72.0.3626.121 on Windows 10
Sounds like your elasticsearch search index is not up to date.
Is your elasticsearch running or is Zammad logging any indexing errors?
When going to admin settings -> Tags, you’ll see a list of tags, if you click on the number behind the tag, it should run a search and give you up to 50 results regarding that. If it doesn’t, your searchindex needs to be reindexed.