Using pipelining with HTTP proxy servers is usually not recommended also because the HOL blocking problem may really slow down proxy server responses (as the server responses must be in the same order of the received requests).

in proxy servers, especially in transparent proxy servers (if one of them along the HTTP chain does not handle pipelined requests properly then nothing works as it should). Most pipelining problems happen in HTTP intermediate nodes (hop-by-hop), i.e. HTTP/1.1 conforming servers are required to produce valid responses to pipelined requests, but may not actually process requests concurrently. HTTP pipelining requires both the client and the server to support it. A sequence of other idempotent requests like PUT and DELETE can be pipelined or not depending on whether requests in the sequence depend on the effect of others. Read requests like GET and HEAD can always be pipelined. Non- idempotent requests such as POST should not be pipelined. By 2017 most browsers supported HTTP/2 by default which uses multiplexing instead. The asynchronous operation of HTTP/2 and SPDY are solutions for this. The speedup is less apparent on broadband connections, as the limitation of HTTP 1.1 still applies: the server must send its responses in the same order that the requests were received-so the entire connection remains first-in-first-out and HOL blocking can occur. The pipelining of requests results in a dramatic improvement in the loading times of HTML pages, especially over high latency connections such as satellite Internet connections. 2.2 Implementation in web proxy servers.

Wireshark http 1.0 or 1.1