I have resolved the problem by adding correct proxy settings at https://XXX.domain.com/webadaptorname/portaladmin/system/properties. The proper settings are
{"httpProxyHost":"Proxyserver.domain.com",
"httpsProxyHost":"Proxyserver.domain.com",
"httpProxyPort":ProxyserverPort(eg 8090),
"httpsProxyPort":8090
"nonProxyHosts":"portalname.domain.com"} .
All required was to find correct "Proxyserver.domain.com" and it is necessary to mention nonProxyHosts value.