Error while trying to set up a one-for-all theme for our GitHub Pages sites

Hi guys,

I was recently asked to update the theme we use across all of our repositories. What we had done previously was to set all of the sites to the Leap-Day theme and then just override the changes we wanted by adding an assets folder with an updated style.scss and a _layouts folder with an altered default.html. This worked fine but whenever we wanted to change something about the theme I would have to go into each of the over 50 repositories and update the files.

Recently I instead copied over the files for the Leap Day theme into a repo and and adjusted it and then set the _config.yml files in all of our repos to point to that repo as a remote_theme. It seemed to work as the sites all still looked the same and built fine until today when suddenly any time anyone made a change to any repo the changes were not reflected on the Pages and they got an e-mail saying

“The page build failed for the master branch with the following error: The tag seo on line 7 in /_layouts/default.html is not a recognized Liquid tag.”

Can anyone explain why this is happening and how to fix it?

The repo for the theme is




Maybe not the best solution but I just removed the SEO plugin altogether.