Cannot access self-hosted domains after updating to V2.7.2.104

I feel like I've just taken off my training wheels and the subject is now Motocross.

My framework is so primitive.

• An app on the computer wants nextcloud.mydomain.org and
  
• Looks in the local DNS cache for the IP address.  oops. not there.
• Sends a DNS query
  (which ordinarily would go to the Orbi, but sometimes people enter static DNS servers)
• That server looks in the DNS cache, oops. not found, and
• Sends the query to wherever it resolves DNS
• Eventually, the domain name is resolved to the public IP of the Orbi router.
• The Orbi gets this connection request and forwards it to the LAN IP of this monster server.
• The server is able to satisfy modern software requirements because it generates suitable SSL certificates.
  (LetsEncrypt/Nginx)

When a device connected over WiFi does this, it works correctly.

When a device elsewhere on the internet does this, it works correctly.

When a device runs VPN software to tunnel out through the Orbi and bypass DNS, etc., it works correctly.

(Using OPenVPN to reach the Orbi LAN is outside the scope of this discussion, correct?)

Only when a device is connected with ethernet, it fails.

I have no clue.  Guess I would put an entry in the local DNS table that points to the local server.  The only alternatives I see are (a) pay Gearhead to open a support ticket, which I have absolutely no expectation would result in anything worthwhile, or (b) do that tedious reinstall of a firmware version that was known to work.