There is a bug when using redact that deletes random alt text in the pdf when the redactions are applied and saved. I tested with files created on my machine and from a third party. Sometimes I could redact one or two phrases and not have any alt text appear. But the more redactions, the more alt text was lost. Sanitize was OFF. The alt text disappeared randomly- sometimes from a page with redactions, sometimes from pages without. Sometimes only one image on a page lost alt text, sometimes all or none did.

To reproduce:
Create an accessible pdf.
Use the accessibility checker to confirm all the figures have alt text.
Make some redactions.
Apply and save.
Use the accessibility checker to see if all the figures still have alt text.

The expected behavior is that they should. No one would expect alt text to be deleted.