And going back to that packet capture. Can you capture an interaction when it succeeds and one when it fails? I looked at it again with a closer set of eyes...
I notice a bunchof non-printable chars. It's possible the stream is somehow getting messed up, which ends up leading to the "500" error and the "not understood" response which happens just before the reset.
So it seems to me that the server gets a command, it doesn't understand the command, and RST's.
That made me look at the Request when i noticed the non-printables. Those might be expected and just fine. That's why I'd like to compare a 'clean' request' to one that fails. Ideally the exact same request where one worked, one failed...
Thanks for sticking with me through this, there's definitely something interesting going on