tag= not working for some tags

This works perfectly
[loop type=goods orderby=date offset=1 count=1]

This also works for some of my tags:
[loop type=goods tag=test orderby=date offset=1 count=1]

Specifically, some tags created and added to posts months ago work. Others created and added months ago return nothing.

If I add one of the tags that “works” to a new post, it returns nothing. All new tags that I create return nothing.

I have reset permalinks, deleted all redirects, and cleared all caches.

How would I debug this?

Thanks, Richard