Why does Tixati v3.29 randomly say "DHT: port unconfirmed" on the bottom status line and other than exiting/restarting Tixati how do I fix this problem?

Tixati hasn't RECEIVED any incoming connections on this port yet. Peers cannot connect to you, only you can connect to peers who have avoided this issue. Your connectivity is impaired.

This is either due to
1. firewall/AV blocking
2. port-forwarding not working
3. ISP doesn't give you an exclusive IPv4 (aka white IP) neither IPv6 to use
4. you are connected to a VPN (see 1 & 2)
5. You use a proxy for Tixati (you shouldn't)

I use Tixati v3.29 and NordVPN on three computers and ONLY have that problem on one of them.

For NordVPN (argh) refer to points 1-3.
I haven't tried to understand the logic of usable ports when behind a VPN. All I can say, without a firewall interfering the rate of success is spurious at best. It is one of fhe reasons you would want configurable and working port forwarding.

The strange thing is though, all I have to do to fix it is to manually close Tixati, wait a couple of minutes and restart Tixati and it magically connects to hundreds of nodes without me changing ANY of my options.  That makes it seem more like a Tixati problem instead of a NordVPN problem.

P.S.
 Same problem in v3.31 of Tixati.

I just noticed after restarting Tixati it connected to over 500 nodes and slowly started losing those connections until it again said "DHT: port unconfirmed"!  It seems to mostly only do that on the computer where I use port #80 for TCP/UDP peer connections and messages.

Try a different port. You shouldn't be using port 80.
and make sure that the port is mapped and mapped correctly.