What would be preventing me from seeing a Tag that we have created and assigned to a Lead when trying to create an Entry Rule within a Series I am building?

I'm building a Series to manage an automated feedback process for our customers. The Entry Rule for this Series will simply be to find any Lead that is tagged "Customer Name Review".

I have created a Lead and given it the appropriate Tag. When I try to create the Entry Rule within the Series, I can see all of our other Lead Tags but not this one.

Other than the tag not being in use (which is not the case), what other factors may be stopping this Tag from displaying as an option to add to the Rule?