primary_category not working

We were unable to reproduce this issue. Please elaborate on the issue you’re experiencing including as much detail as possible such as a link to the site in question, the expected outcome, any errors you received, steps to recreate the issue, and, if possible, screenshots.

I looked into this further and perhaps what I’m expecting was never a part of how Title meta %%primary_category%% ever worked.

I assumed a post with only a single category selected would be noticed as %%primary_category%% in the Title meta.
Is that not the case? Or did that stop working for me?

%%primary_category%% does work and does appear in title meta when there are more than one categories selected and one is specifically selected using “Make Primary”.

Thank you

When selecting a single category, that category is also set and output as the primary category. Sometimes strange behavior may be caused by a plugin or theme conflict. The fastest way to rule out conflicts is to deactivate all non-Yoast plugins and switch to a standard theme like Twenty Sixteen. If this resolves the issue, you have a conflict and should activate one plugin at a time until you locate the conflict. Finally, after all plugins are active, switch to your theme. This will narrow down the conflict to a specific plugin or theme.

If you are unfamiliar with checking for conflicts, we wrote a small guide that will walk you through the steps. You can find it here: How To Check For Plugin Conflicts