Hi Ilya, I think this time I managed to fix the ABNS test. To make a long story short, it was by design extremely sensitive to the new process's startup time, which is increased with larger FD counts and/or less powerful VMs and/or noisy neighbors. This explains why it started to misbehave with the commit which relaxed the maxconn limitations. A starting process stealing a few ms of CPU from the old one could make its keep-alive timeout expire before it got a new request on a reused connection, resulting in an empty response as reported by the client.
I'm going to issue dev5 now. s390x is currently down but all x86 ones build and run fine for now. Cheers, Willy