Acrobat standard 2017 missing characters when saving the document

The company I work for has 10+ installs of Acrobat standard 2017, and I have ended up resintalling them when this issue comes up on them.  Windows 7 professional on a domain system.  The problem is that when the problem comes up the only solution I've found is to uninstall completely and reinstall Adobe Acrobat.  Basically the users are editing scanned documents with Acrobat, and then one day the files they edit are missing characters that they type in using the text tool.  Or corrupt text fonts.  Thing is we use basic arial font for all edits.  Nothing special.  I have been unable to find anyone else with this issue.  Over the last year I've reinstalled all of them at least once.