Keep getting DHT: Port unconfirmed and Started - Unconfirmed incoming port. This happens for a while, then magically fixes itself for a time. Any way to keep this from happening?

Do you use a router and a modem? If so, you need to set the modem to bridged mode. It is hard for two devices acting as shields to get along, but they will after some time. That getting along stops as soon as the transfer stops and then they learn again for the next transfer. Your router will offer you the protection from intrusion on its own the modem does not need to also act as a firewall.

I am having a similar problem here DHT is OK and connected and then goes to Port Unconfirmed.  My router is UPNP enabled, I have turned off Windows firewall and that makes no difference, and the LAN cct does go through a switch but there is nothing in there that should cause any problem.

Not sure what changed in my setup that is causing the problem and at a loss from incremental diagnosis point of view

I have same problem...DHT will connect and work for awhile then ill go to Port Unconfirmed.  Router is set to UPNP, firewall is not blocking, and nothing has changed in my setup other than I upgraded to a 50M DSL service.  Perhaps my ISP is doing something different?

At a loss in terms of further diagnostics so looking for advice

In Tixati click on home. There you will see a log, look for errors. IE it will say udp or tcp  "looked to the router but no response". Sorry forget the exact words. It will say no routers responded. My experience with this was that my router was not reliable under UPNP. I configured it(router) to forward the port directly.
  There is a tool and help for all routers at portforward.com. It is important to download the port check tool and run the tests. They need to be run under UDP and TCP although the port unconfirmed is a UDP error.

Also while on the Home page in Tixati look to the lower right corner. Under incoming connections look at the numbers for received and placed. If you have a large "received" number that will tell you that likely TCP is getting through, If it is a small number then neither TCP or UDP have reliable connections.

When I had my problem first it was my modem but I had other things wrong.

How much would be large?

Large is relevant to the number of torrents you have running. 4hrs since I opened my program I have 23,000 incoming and 6000 out going. I am connected to 150 peers and there are 800 on the list. Aprox. of course. So in ten minutes check how many peers you are connected to and look at the in and out, combined that should be more than the peers you are connected to, not how many are on the list though.
It counts one every time you connect to a peer, even if it a reconnect because you dropped a peer and they call back.