Try increasing the sync timeout -
Channel Specific Timeout Configuration (Synchronous Interfaces)
PI/XI: PI 7.3 new functionalities for different adapters (JMS, JDBC, HTTP) - teaser
Also Refer to SAP Note : 856597 - FAQ: XI 3.0 / PI 7.0/7.1/7.3 SOAP Adapter
- Can I configure the timeout value of my receiver adapter?
A: Yes. The default timeout value for outbound calls is 5 minutes. You can increase this value by setting parameter XMBWS.Timeout in the module parameter table of the SOAP adapter. The value must be given in milliseconds. For example, value 600000 represents the timeout value of 10 minutes. This parameter is not recognized in systems prior to SP13.