Thank you for your post!
After reading through the thread and the cases created from the customers, this has been caused by corruption. Damage in a Database File can cause any number of unexpected behaviors. I would recommend running Recover on the files to check for said damage. You might also Save a Copy of your file as a Clone and see if issues persist there, then reimport your data.
Also see: What to do when your file is corrupt
Let me know if you have any further information!