The borders on tables in Microsoft Word keep disappearing for all people in my company

• Is this happening with all Word documents or only specific ones? 
  • I don't know about ALL, but it's happening in multiple shared Word documents.
• Are the borders missing in Print Preview or just on-screen? 
  • It's not just the borders, the entire custom table setting seems to be wiped. It loses the formatting - borders, font color, background color, font size, paragraph and row settings.
• Does the issue persist when opening the document in Word Online? 
  • Yes.
• Where is the file saved on OneDrive, SharePoint, or locally? 
  • For the ones where I've seen it, saved on SharePoint. But that's where we share documents, so it would be where I'd see it.
• Have you check if there anyone who might have modified the file? 
  • Yes, initially it looked like that might be part of the problem, but it wasn't we've found it now in documents that only one person had edited to set the table style and then when back a little later and the style was wiped. (There's still a table showing in the custom table styles section, but it doesn't have the style formatting - just the name of the custom style shows if you hover over it.)
• If the file is share for other user to edit it could you check the history version to see what the user have edit in the file?  You should turn on the Track changes for everyone. 
  • Track changes was on for everyone. As noted above, this occurs even when no one else has edited/changed the file since the person set the table style and used it. While it's possible someone else opened the file, this has happened now on enough files that were left during non-working hours that I can be fairly sure no one else even opened them between the time the first person set the style and then the same person when back in and found the style lost.

Our issue is similar to the thesis writer, we have documents that are hundreds of pages long with many tables, and it's a major problem when you fix all the formatting and come back to the file the next day to find that all the tables are messed up AGAIN!

I am due to submit my PhD thesis very shortly and this removal of table borders is disastrous. We've seen these intrusive errors after updates before but would appreciate MS working it out and not letting it happen again

Do you see this in Word Online (OneDrive and/or SharePoint)? If you download the document and view it in a local installation of Word, does the problem persist?

If possible, share such a problematic document with the forum so that we can have a closer look. Of course, any personal information should be removed from the document before you share it.

You may also want to report this to Microsoft, via Help > Feedback.

Table styles in Microsoft Word keep disappearing when the file is shared on a SharePoint site and multiple people are viewing/editing said document.