I have a similar issue when I use the java/ws-rawclient protocol and I have not gotten any closer to a permanent resolution.
My issue, the destination confirms receipt of the message and correct mapping in their system, but they send a 202 http response (accepted – not yet processed) which I would’ve thought was an acceptable response for Cloverleaf(?).
In the interim while I am still investigating, I am having the destination system send a 200 response if it gets the message and does not error. That stops the engine from queueing and the error does not happen. Although I believe there is a bigger issue than just the http response being “off” to cause that java error.