Excel 2010 Shared Workbook error messages

I got your name from the http://www.mvps.org website and would appreciate any help you might give on my problems.

A [Shared] workbook stored in a shared folder on the network. 12 Users are sharing the Excel file.
Excel 2010, Windows 10, All updates are current. 2 users are on Excel 2013

Thank you in advance for your time. I have one issue and one puzzlement in this shared workbook.

Issue: A user receives the following error message when they try to save their updates.

[Excel was unable to save the workbook because there was a problem reading or applying part of the revision history. You can unshare the workbook or save to a non shared workbook format to fix the problem.]

What is causing this error and how can it be resolved? Sometimes it locks the user out and they have to close the workbook and consequently lose their updates. Or they can only save the workbook with a new file name and that in itself creates a huge problem.

Puzzlement: When the workbook owner looks at the following dialog box, they see this.
Review tab > Share Workbook > Editing tab.

Note that 2 users, Brian Horne and Jason Jones, show the workbook being open on two different dates days apart.

Is this normal? I would think that you can only see one instance of the workbook being open.
Could this be causing the error message above?

Best regards,