There are certain things to take note of if your qRFC communication contains update steps. The serialization behavior changes depending on whether you are dealing with a tRFC or qRFC call.
If you use tRFC calls within the same transaction in both dialog steps and update steps (CALL FUNCTION ... IN UPDATE TASK), then the sequence of the tRFC LUWs is undetermined, that is, they are assigned to different LUWs and get different TIDs.
If you are using qRFC, you can, for example, call function module TRFC_SET_BACKGROUND_SEQUENCE in your transaction to specify the processing sequence.
Note
The function module is contained in qRFC API for the outbound queue.
If you do not explicitly set out a sequence, the following behavior is default: All qRFC calls from the dialog step are processed before the qRFC calls from the UPDATE TASK.