Hi,
Thanks for the details.
The live search response from the server is completely missing indeed, but there is no error code, nor anything in there. In fact it reports successful response, which is very unusual when there is no response body.
Are there any firewall/cache plugins active, that could temper with the page contents? Can you please try turning them off, to see if that makes any difference? I suspect that something is removing/catching the request body – perhaps a firewall filter or something similar.