Thanks for posting.
It’s unlikely/impossible that Mastermatic has just stopped working.
So the issue is almost certainly a problem with the document in question, or else perhaps the way you’ve set up Mastermatic options for this document.
Could you upload some screenshots that show (a) your Mastermatic setting (both for the main tab and object-master tab), and (b) perhaps a screenshot of a document page that shows an incorrectly applied master page. Explain what master page you were expecting to be applied, and which is actually applied…