Illustrator 24.2.3 crashes at exit, cannot see contents once 2019 file is opened, preview displays

Illustrator 24.2.3, cannot open a file for editing that worked fine in earlier version of  Illustrator, probably CC 2019, to make a change. A preview is displayed before opening. Fortunately CS5 can open it, otherwise I would have lost a customer. After closing 24.2.3, it crashes about 50% of the time. The CS5 versions of files were produced by using CS5 to open the CC 2019 versions, although it complained that they were newer and might not have valid text attributes, and saving to CS5 format. The eps and TIF are used by the tray card. The 2up has the tray card positioned for printing on a special stock. This is a bug, not a feature! All files are local to my Windows 10 PC running Illustrator.

And this forum does not let me attach the AI file! They can be found for the next 3 months at: https://spaces.hightail.com/receive/oLWByJdt8v 

Correct the highlighted errors and try again.

• The attachment's traycard-2up_my old armenia r2 cs5.ai content type (application/postscript) does not match its file extension and has been removed.
  The attachment's traycard-2up_my old armenia r1.ai content type (application/postscript) does not match its file extension and has been removed.
  The attachment's my old armenia tray card r4 ready for printing cs5.ai content type (application/postscript) does not match its file extension and has been removed.
  The attachment's my old armenia tray card r4 ready for printing.ai content type (application/postscript) does not match its file extension and has been removed