NPOI sometimes only reading 10 lines from a spreadsheet

Question

PROBLEM: I've hit a troubleshooting wall and hoping for suggestions on what to check to get past an issue I'm having with an internet site I'm working on. When reading data from a spreadsheet using NPOI (C#), sometimes (not all the time) the row reading stops after just ten rows.

Sorry for the very long post but not sure what is/isn't useful. Primary reason for posting here is that I don't know the right question to ask the Great Google Machine.

I have an intranet site where I'm reading an XLSX file and pushing its contents into an Oracle table. As you can tell by the subject line, I'm using NPOI. For the most part, it's just working, but only sometimes...

In Oracle, I have a staging table, which is truncated and is supposed to be filled with data from the spreadsheet.

In my app (ASPX), users upload their spreadsheet to the server (this just works), then the app calls a WebMethod that truncates data from the Oracle staging table (this just works), then another WebMethod is called that is supposed to read data from the spreadsheet and load the staging table (this, kinda works).

It's this "kinda works" piece is what I need help with.

The spreadsheet has 170 data rows. When I run the app in VS, it reads/writes all 170 records most of the time but sometimes it reads just 10 records. When I run the app from the web server, the first time it fails (haven't been able to catch a specific error), the second and subsequent times, it reads just ten records from the spreadsheet and successfully loads all ten. I've checked the file uploaded to the server and it does have 170 data records.

Whether the process reads 10 records or 170 records, there are no error messages and no indication why it stopped reading after just ten. (I'll mention here that the file today has 170 but tomorrow could have 180 or 162, so it's not fixed).

So, I've described what it's supposed to do and what it's actually doing. I think it's time for code snippet.

        /* snowSource below is the path/filename assembled separately */
        /* SnowExcelFormat below is a class that basically maps row data with a specific data class  */

        IWorkbook workbook;
        try
        {
            using (FileStream file = new FileStream(snowSource, FileMode.Open, FileAccess.Read, FileShare.Read))
            {
                workbook = WorkbookFactory.Create(file);
            }
            var importer = new Mapper(workbook);                
            var items = importer.Take<SnowExcelFormat>(0);
            /* at this point, item should have 170 rows but sometimes it contains only 10 with no indication why */
            /* I don't see anything in the workbook or importer objects that sheds any light on what's happening. */

Again, this works perfectly fine most of the time when running from VS. That tells me this is workable code. When running this on the web server, it fails the first time I try the process but subsequently it runs but only picking up that first 10 records, ignoring the rest. Also, all the data that's read (10 or 170) is successfully inserted into the staging table, which tells me that Oracle is perfectly okay with the data, its format, and this process. All I need is to figure out why my code doesn't read all the data from Excel.

I have verified numerous times that the local DLL and webserver DLL are the same. And I'm reading the same Excel file.

I'm hitting a serious wall here and have run out of ideas on how to troubleshoot where the code is failing, when it fails. I don't know if there's something limiting memory available to the FileStream object causing it to stop reading the file prematurely - and didn't run across anything that looked like a resource limiter. I don't know if there's something limiting the number of rows pulled by the importer.Take method. Any suggestions would be appreciated.