A $%&sdbatch is often created in "simultation'" mode from some transaction/BAPI (or FM kie ISA_LOCK_SALESDOCUMENTS in its call of SD_SALES_DOCUMENT_ENQUEUE which wrap the final ENQUEUE_EVVBAKE), so check your code did you use one of those FM
Did you also check lifetime of the RFC connection, if connection close (explicit RfcClose or inactivity time, etc.)
Regards,
Raymond