As you have already tried different parameters, I would suggest to check timeout option for ICM and Web Dispatcher.
In SAP, you have ICM and Web Dispatcher with different timeouts, controlled by different parameters:
SAP Recommendation for these scenarios:
In systems where the standard timeout setting of 60 seconds for the keep-alive and processing timeouts is not sufficient due to long-running applications, SAP recommends that both the TIMEOUT and PROCTIMEOUT parameters are set for the services concerned so that they can be configured independently of each other. The TIMEOUT value should not be set unnecessarily high. We recommend you set this parameter as follows:
icm/server_port_0 = PROT=HTTP, PORT=1080, TIMEOUT=60, PROCTIMEOUT=600
in order to allow a maximum processing time of 10 minutes.
You can refer SAP Help portal to check Time out options for ICM and Web Dispatcher.