I'm not sure if I fully understand your question Eduard, but the token itself, internally, is built by the original request's Message Header ID (and the Production name; concatenated with a pipe - |)

E.g., from the code (in Ens.Host):

Method GetDeferredResponseToken(pMessageHeader As Ens.MessageHeader) As %String
{
    Quit pMessageHeader.%Id()_"|"_$$$EnsRuntime("Name")
}

ClassMethod SendDeferredResponse(pDeferredResponseToken As %String, pResponse As %Library.Persistent) As %Status
{
    Set tSC=$$$OK
    Try {
        Set tMessageHeaderId=$p(pDeferredResponseToken,"|",1)
        Set tProductionName=$p(pDeferredResponseToken,"|",2)

Note this is of course internal implementation, and I don't think it is documented or supported (i.e. might change in future versions without notice).

Thanks for filling in the picture Michael.
So this seems to fit into the theory I had about the error indicating your SOAP client is not receiving the response it expected.

You can see the server (the SOAP service) you are turning to is running into an internal error (HTTP status 500) and you also have details about the error they ran into "javax.... " and their relevant stack.

I suggest, if it is possible, that you turn to the entity that is behind this service and report to them the error you are getting (makes sense also to share with them what you see in the log that you are sending to them).

And they might be able to help you.