13.1R problems on Pi3

A clean install of 13.1R on a Pi3 still exhibits three long-standing
problems also seen on a Pi3 which started from 13.1RC4

Attempts to saveenv under uboot running from microSD fail.
As it happens, I need to set usb_pgood_delay to a larger
value to let the machine find the USB hard disk. Thus far
the workaround has been to manually editenv on the console.

Inbound ping requests are not answered except for a few
seconds around the time ntp runs.

Inbound ssh connects prompt for a password and then time out.

The ping and ssh problems can be worked around by starting an
outbound ping process. A few seconds after doing so both ping
and ssh are answered, erratically but usably.

The problem seems to be confined to the Pi3s. Four Pi2s and a Pi4
on the same network branch exhibit no such problems. Only the
pair of Pi3s seem to be affected, under 13.1 and -current.

The network is started with these lines in /etc/rc.conf:
 
hostname="www.zefox.org"
ifconfig_ue0="inet 50.1.20.28 netmask 255.255.255.0"
defaultrouter="50.1.20.1"
sshd_enable="YES"

Reference to DHCP has been removed. Could that be a source
of mischief? It seems not to cause problems on other hosts.

Thanks for reading, any insights appreciated!

bob prohaska