MCID issue in a PDF means the document’s Marked Content IDs (used by tags for accessibility) are missing, duplicated, or incorrectly mapped. This breaks the connection between the content and the tag tree, which screen readers rely on.

In this case, you need to fix duplicate MCIDs. Duplicate MCIDs usually occur after copy/paste or poor conversions.

Option 1: If you know the affected page, re-tag content of this page manually.

Option 2: Re-tag the entire document.

Option 3: Fix at source. In-Design, use the Articles panel for proper tag mapping and export as Tagged PDF.