Some odd TCP behavior (timeouts)

Hello, 

I'm having a TCP connectivity issue stumping me and driving me crazy.
The TLDR version: No more printing on my LaserJet (but ping works),
while printing and the web interfacw works fine under Windows.
Other TCP connections apparently flawless.
Wireshark shows FreeBSD performing the three way handshake but
then ignoring some packets sent from the printer (no ACKs)
and retransmitting until timeout hits.
 
The details with the wireshark logs are on 
https://superuser.com/questions/1649435/mysterious-tcp-http-issue-accessing-laserjet-web-interface

I have seen a few commits to CURRENT's tcp and timeout code recently.
I went back to stable/13 as of two days ago, but still no joy.

Has anyone else noticed something going on with TCP?
Especially HTTP/HTTPS, like connections timing out in rare cases?
If you have a LaserJet (preferably 551dn), can you still access
its web interface, or get a reply with

  printf "GET / HTTP/1.0\r\n\r\n" | nc LaserJet 80   # or 443.

Regards,

        Jens
-- 
Jens Schweikhardt http://www.schweikhardt.net/
SIGSIG -- signature too long (core dumped)