Created attachment 298007 [details]
A basic repro of the observed issue.
We see an unexpected pause of 3-60 seconds where the test no longer receives data, recv() is blocking, netstat shows data is sitting in the 7777 server's send queue and 0 bytes are in the test's receive queue.
Setting net.core.rmem_max seems to be a key factor. For our testing we used net.core.rmem_max=16777216
See attached README and repro.