I've tried a few other things with no avail at
this point.
Put a monitoring device at the outside port, or start a data capture in the router itself
when EdgeOS can
do that, and then check what is arriving when you do the outside ping.
When you see packets coming from 169.228.66.251 addressed to your external IP with
protocol field 4 you
at least know the external causes are covered. You can then concentrate on the setup of
your router.
When no such packets appear, the problem is in your gateway setup at
portal.ampr.org or
your DNS entry.
As I don't see your callsign or AMPRnet IP anywhere in your message I can't do
much research...
Rob