Pi3 answers ssh only if outbound ping is running on -current

From: bob prohaska <fbsd_at_www.zefox.net>
Date: Sat, 12 Feb 2022 18:56:18 UTC
For a few weeks now a Pi3 running -current will not respond to
an incoming ssh connection unless an outbound ping process is  running.

Once the outbound ping is started via the serial console, incoming
ssh connections are answered normally. Uname -a reports
FreeBSD www.zefox.org 14.0-CURRENT FreeBSD 14.0-CURRENT #10 main-n253073-6db44b0158c: Sat Feb 12 04:30:21 PST 2022     bob@www.zefox.org:/usr/obj/usr/src/arm64.aarch64/sys/GENERIC  arm64

A Pi4 running -current of a few days ago exhibits no such problems.

Another Pi3 running stable/13 has been behaving in the same way.

Both Pi3s successfully set time via ntp on reboot and will
very briefly (one or two minutes) prompt for an ssh password,
but no further progress is made and the login attempt times out.
If the ssh login is attempted a second time, not even a password
prompt comes back.

Ping times (to an adjacent machine on the same subnet are
64 bytes from 50.1.20.26: icmp_seq=2 ttl=64 time=0.978 ms
64 bytes from 50.1.20.26: icmp_seq=3 ttl=64 time=0.967 ms
64 bytes from 50.1.20.26: icmp_seq=4 ttl=64 time=1.088 ms
64 bytes from 50.1.20.26: icmp_seq=5 ttl=64 time=0.983 ms
64 bytes from 50.1.20.26: icmp_seq=6 ttl=64 time=1.007 ms
64 bytes from 50.1.20.26: icmp_seq=7 ttl=64 time=1.075 ms
64 bytes from 50.1.20.26: icmp_seq=8 ttl=64 time=1.020 ms
64 bytes from 50.1.20.26: icmp_seq=9 ttl=64 time=1.044 ms
64 bytes from 50.1.20.26: icmp_seq=10 ttl=64 time=1.026 ms
64 bytes from 50.1.20.26: icmp_seq=11 ttl=64 time=0.908 ms

That might be considered slow, but the correspondent machine
is only a Pi2 running 
FreeBSD www.zefox.com 14.0-CURRENT FreeBSD 14.0-CURRENT #3 main-71d2d5adfe: Tue Dec 21 00:23:51 PST 2021     bob@www.zefox.com:/usr/obj/usr/freebsd-src/arm.armv7/sys/GENERIC  arm

If the outbound ping is started, an incoming ssh connection established
and the outbound ping subsequently stopped the running ssh connection
silently freezes; no disconnect, but no response, not even echo. Some
tens of seconds later, all inputs were responded to. Tried a second time,
the stoppage recurred, restarting the outbound ping eventually restored
responsiveness.

With the outbound ping stopped, an inbound ssh attempt silently failed:

bob@raspberrypi:~ $ ssh -vvv 50.1.20.28
OpenSSH_7.9p1 Raspbian-10+deb10u2+rpt1, OpenSSL 1.1.1d  10 Sep 2019
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug2: resolve_canonicalize: hostname 50.1.20.28 is address
debug2: ssh_connect_direct
debug1: Connecting to 50.1.20.28 [50.1.20.28] port 22.
[enter key echoed]
debug1: connect to address 50.1.20.28 port 22: Connection timed out
ssh: connect to host 50.1.20.28 port 22: Connection timed out
bob@raspberrypi:~ $  

Thanks for reading and any insights. If I've omitted useful 
details or tests please indicate.

bob prohaska