missing ARP reply

I'm having trouble with my solar inverter connecting to its home base
somewhere in Germany and am suspecting a problem with a missing ARP
reply.  Traceroutes go most of the way there, and individual power
optimizers appear to be reporting successfully so they are clearly
getting through, I assume via a successful DNS translation in the
inverter software.  Or maybe the inverter itself is sending out the
optimizer info (I thought that was how it worked).  But the monitoring
site claims the inverter itself is not reporting. (SolarEdge system
if anyone cares).

xxx.yyy is the inverter on the local network
xxx.zzz is the fbsd gateway/router on the local network

#tcpdump -flnt -i fxp0 | grep 192.168.xxx.yyy
ARP, Request who-has 192.168.xxx.zzz (aa:bb:cc:dd:ee:ff) tell 192.168.xxx.yyy, length 46
IP 192.168.xxx.yyy.3337 > 147.185.237.1.22222: Flags [.], seq 26043:26065, ack 708198036, win 2144, length 22
IP 147.185.237.1.22222 > 192.168.xxx.yyy.3337: Flags [P.], seq 1:23, ack 22, win 18410, length 22
IP 192.168.xxx.yyy.3337 > 147.185.237.1.22222: Flags [.], ack 23, win 2144, length 0

I'm guessing the 3 packets exchanged are a power optimizer reporting in,
but may be the inverter doing something.

The arp table on xxx.zzz has a permanent entry for itself on the interface,
picked up from /etc/hosts:

# arp -a
ns.dreamchaser.org (192.168.xxx.zzz) at aa:bb:cc:dd:ee:ff on fxp0 permanent [ethernet]

Thoughts on why I am not seeing a reply to the ARP request?

Thanks,

Gary