Which version of NaviServer are you using? There was a change in timeout semantics this year, making the behavior more useful.
How does backend behave? Does it send data incrementally or long time nothing and all data together?
For answering these questions, you can use in revproxy-procs the "verbose" flag, and "ns_logctl severity Debug(connchan) on" (e.g. in ds/shell) to get low-level debug information.
[1] https://bitbucket.org/naviserver/naviserver/commits/177e4e66a54810ed0bf4434ed0e60510584e3b90
