Hello Netta,
This happens because metadata information is cached. Metadata is cached because metadata is data about structure of db which is not very frequently changed. And after ceeation of metadata cache you added table or columns.
When you login from the home page you can delete the datasources cache (below image). Then it will work

Then, go to the metadata page. You can edit the metadata or create new metadata. Click on this refresh option

You will be able to see the additional tables. If that specific table is already added, click on “Reload” option and when you expand now it will show additional columns also.
Thank You,
Helical Insight.