SAP GUI: Failed to set the PO (Purchase Order) number error during load test in Controller

Hello,

I have LR - 11.50 installed on Windows, SAP GUI version is 7.20.

I have set the PO number to be unique such that

{unique} set in Parameter as date/Time as %d%H%M%S.

{rand1} set in Parameter as random number in the range from 1 to 1000.

sapgui_set_property(txtVBKD1, "text", "OBD{rand1}{unique}", LAST );

I even tried with sapgui_set_text function but around 40% - 50% of the trasactions fail on setting this PO number in the text field.

I ran the script in Vugen with 15 users and all passed. Only when I run the script in Controller with over 135 users then the failures are seen.

Kindly advise solution for this.

Thanks.