Resolution:
Users have the ability to log outbound transactions in designated directories that are configured by BC.  The file names for these transactions are configurable via a file mask, which can incorporate parameters such as the trading partner name, the current time, etc.

Under heavy load, it is possible for multiple outbound files to be generated with the same file name.  If this happens, BC can overwrite a previous transaction logged in the directory.   It then appears that BC did not save certain transactions.

To eliminate this issue, make sure that you include the GUID parameter (Guaranteed Unique Identifier)  in the file mask, by using "#(guid)" in the file mask.  This will force BC to put a unique identifier in the file name, and prevent any files from being overwritten.

Outbound batch transaction appear never to be saved or get overwritten in the logging directory for BC.