Problem solved!! The insight you provided me about the Kenwood protocol provided a solution, or at least a satisfactory work-around.
The band jumps (or amp fault mode) are due to the VFO B setting. If I sync the VFO's , I can avoid the problem. Still doesn't explain why band info is being sent when ...

The 1306 will only respond to bandswitching if the "Allow Kenwood AI Command" is checked. Perhaps you did not have this activated when you checked with your setup?

No need to apologize for the delay in response. I and everyone else, I am sure, are very grateful for everything you are doing with this forum!

Before running the terminal emulator app, I did a fresh installation of Thetis (including new FFT calculations) and also reinstalled the firmware. There ...

Although I am sure it is trivial for some, I have not used a terminal emulator program before so I am having difficulty setting it up. Of course I defer to your expertise if you feel this information is critical. It is acting, however, like it is sending 40M band data as the jumps are not random ...

Is the use of DDutil a requirement? That certainly would explain things. As I said in my original post, I often miss the obvious, but did not see anything in the manual about the necessity of using DDUtil (and it works pretty well without it!).

It will switch to 40M and stay there until re-clicked. If 40M was originally selected, then clicking those items does not cause a band jump.

I agree this is probably a Thetis issue. It is easy enough to check out with voltmeter/scope on pin 3 of the serial connector.

Using Thetis v2.8.11 with a 200D using protocol 2 with v1.8 firmware. Works great (!) except for a slight problem with running CAT control for bandswitching an ALS 1306 amp. It changes bands appropriately, but clicking on TUN, PS-A, or RIT causes a band jump that needs to be corrected by "re ...