EDIINT not recognizing payload sender id

I’m on WM 6.1 and have a partner sending us 2 EDIINT files 1 right after the other (20 seconds apart). Both EDIINT file types are recognized and the sender is recognized. When the payload of the 1st EDIINT file is sent to TN the sender id is not recognized, but the payload of the 2nd EDIINT file that is sent to TN the sender is recognized. When I manually submit the payload from the 1st EDIINT file the sender is recognized and is processed successfully.

Does anyone know why the sender id of the payload of the 1st EDIINT file would not be recognized?

the EDIINT type is application/pkcs7-mime
My partner said that both EDIINT files maybe sent within the same connection.

Any help would be greatly appreciated