Text is being changed after running accessibility checker

I have come across this multiple times, but it is not an extremely common issue. On different documents, after I run the accessibility checker, then do the Fix for tagging, it will either add random characters to the end of sentences/lines or it will totally delete sections of text. I am required to make all of our documents accessible, but if by using the fix for tagging is altering the document in any way (and these are only ones I have caught) then I don't know how to fix the 508 compliance issues.

I believe it may be a font issue, because for one document, I was able to convert it to a Word document (before tagging) and change all of the font to Calibri, then convert it back and it did not delete any of the text after that. However, that was a mostly text document with simple formatting. People submit documents all the time that are hundreds of pages long and/or are collated from different sources or designed using unique fonts and have very complex formatting, and I'm not always catching the added characters, or more importantly, the deleted text after I run the tagging fix.

I am attaching 2 documents, one is before I run the accessibility checker. The other is after I run it and fix the tagging via Tagged PDF- Failed fix method. On the second page, the header for the table has disappeared in the POST 508 file. I had no idea it was missing, until a user who is familiar with the document reported it.

I have had this happen on simple agenda documents (added characters), complex budget documents (removed numbers and other text), as well as a few other documents. Liek I said, it is not a super common occurence, but it has happened multiple times on various documents.