Issues Involving Sharing Workbooks

Hello. I am unsure whether this would be the proper place to post this issue, but here goes.

My office uses Excel 2010 and have two separate workbooks that are shared out to the users in their respective departments. The purpose of this being that multiple users need to access/edit these documents frequently throughout the day at the same time. This has worked perfectly for us for about five months now until last month when errors began popping up. For example, the first error that occurred was that our shipping/receiving log actually jumped from 200KB one day to 46MB the next. At some point over one million rows were added to this document in one fell swoop. Obviously, this caused major issues regarding the functionality of the workbook. This was quickly fixed by creating a new workbook and copy/pasting the useful info into the new document.

The latest example which just began two weeks ago is a bit less convenient. Regarding the S/R Log, when our S/R supervisor finishes working on it and then opens it on another workstation to review with his manager, the data seems jumbled but only in spots. For instance, he will enter a phrase in cell A4 and when it is opened on the manager's workstation, this phrase may appear in B7, E5, G1, etc. No particular pattern. Seemingly no rhyme or reason. The document used with our Engineering Dept is commonly edited and saved by that manager, then the users in the department frequently open the document to review the changes. The document seems to lose formatting when opened on two of the four machines while opening just fine the next moment on the other two machines in the department. In particular, it loses the specifically set sort row.

I have confirmed that all machines in the building have the same version of Excel 2010 as well as having been fully updated. This would not seem to be the culprit, unfortunately.

Is there a known issue with the sharing function in Excel 2010? Is there an add-on that could be installed to help with the sharing functionality?

Thanks for any help.