Hi Leo,
Based on your description, since equations created previously remain visible while newly inserted equations disappear when saving or printing, this appears to be a recent rendering or saving issue in Word for the web, rather than a problem with your printer.
As an immediate workaround, I recommend trying the following:
- Create a backup copy of your document.
- In Word for the web, select Editing > Open in Desktop App.
- Check whether the newly inserted equations remain visible in the desktop version of Word.
- If any equations are missing, recreate them using Insert > Equation, then save the document in .docx format.
- Export the file using File > Save As > PDF, or print directly from the desktop application.
If you don't have access to the desktop application, please try opening the document in a different browser or in an InPrivate/Incognito window as a temporary test.
You can also review File > Version History and restore a version from before the issue began, provided the document is stored in OneDrive or SharePoint. For more information, please see: View previous versions of Office files.
In the meantime, I recommend avoiding further edits to the original document until you've created a backup copy, as newly added equations may not be preserved correctly.
If possible, please let me know whether the equations also disappear after downloading the document as a .docx file and opening it in the Word desktop application. This will help determine whether the issue is limited to Word for the web rendering or whether the equations are not being saved to the document itself.
I hope this helps point you in the right direction. If you need any further assistance or have any concerns, please don't hesitate to reach out.