I'm experiencing strange behavior with HTTPS connections from my Debian system to several servers in applications that use OpenSSL 1.1.0, including Python.

I can reproduce the issue with e.g. echo 'GET / HTTP/1.0\nHost: pintan.santanderbank.de\n\n' | openssl s_client -quiet -connect pintan.santanderbank.de:443. With OpenSSL 1.0.2 this just displays the HTTP response followed by read:errno=0 and terminates as expected. With OpenSSL 1.1.0 the connection does not get closed and the server sends the response over and over again in an endless loop. I didn't see the encrypted alert I'd expect the server to send in Wireshark.

I have no idea what I'm actually experiencing there and if it's really an issue with OpenSSL (probably in connection with a specific server-side library). The versions I tried are 1.0.2k and 1.1.0d Debian packages.