Yea, me neither. So, what happens is if you go to /news/newsletter/2012 it just resolves back to /news/newsletter and only shows the current year. Not quite sure how to troubleshoot this, all I know is it seems that after WP 5.5 people started complaining online about this pagination issue, yet I am coming at this issue a few years late so am not finding a whole lot to go on here.
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