I tried to change the client connection point address of the WebGateway, but still no success.
Eventually it appeared to be an Apache Config problem.
In <Apache_Install_Dir>/conf/extra/httpd-mpm.conf there is a setting.
# worker MPM
# StartServers: initial number of server processes to start
# MaxClients: maximum number of simultaneous client connections
# MinSpareThreads: minimum number of worker threads which are kept spare
# MaxSpareThreads: maximum number of worker threads which are kept spare
# ThreadsPerChild: constant number of worker threads in each server process
# MaxRequestsPerChild: maximum number of requests a server process serves
The important setting here is StartServers. This value MUST be "1".