Hi,
With reference to the volume of customers, one of our larger Adagio sites with over 50,000 customers has never experienced the situation you are describing, so we do not think that the volume of customers is an issue.

The same for volume at another of our Adagio sites with over 90,000 inventory items. No accuracy issues when exporting to Excel. Takes a bit of time for the export to complete, but the resultant is complete and accurate. They would like the export to be faster but considering the volume, the speed makes sense.

Exporting at volume sites used to be an issue with number of line limitations on older versions of Excel, but not with current versions.

Your environment sounds like a situation of your older workstation (with the problem) being an XP, running an older version of XLS, with OP locks disabled on the workstation, with SMB2 setting on your server, (I'm guessing 2008 Server.) Which would be less than optimal settings for the workstation. More details would help, but my gut feel says this may be contributing to the cause.

Best,
Brian