Answers to the questions - and / or comments:

 Do you Stop monitoring and Halt Tx before a band change?
> No,  I didn't need to stop monitoring in prior versions.  I never change bands during a TX so the 2nd part of that question doesn't apply.

> The RFI question doesn't apply because I'm never transmitting when this happens.  The PTT method I use is CAT. The radio goes into TX with no issues, but there's just no audio.

R: So after changing the band you have received a full timeslot to spot somebody and double-clicked his call, I assume. And your Tx has gone to transmit at the beginning of next appropriate TX cycle, but no audio. After noting that you use “halt Tx” and “Enable Tx” and still no audio. Or did I missed something? Or do you have “Double-click on call sets Tx enable” unticked and you use “Enable Tx” to invoke transmission?
>Your assumption is correct.  I'm waiting for a callsign to show up - after a decode - than double clicking on it to initiate a response, and yes during the beginning of an appropriate TX cycle.   The second part of your question is no longer valid, as I've discovered that a "halt/enable" cycle does restore audio during TX.

Does this “no audio after band change” happen also, when you try to send a CQ in the next available Tx period after band change? I assume that there is no confusion about “Tx even/1st “ and which time-slot is used for transmission.
> I don't know, because I always listen for other stations and respond after a band change.  I understand the "TX even/1st" concept.   I've been using this program for well over a year and haven't had any issues until 2.3.0.

I have assumed that audio is sent at the same time as CAT has commanded PTT on. By the way which PTT method you are using and which rig we are talking about? We have some unknown issue in your system.
>As I have answered or provided before, I am using CAT control to command PTT.  The rig is an ICOM 7300, I now know of at least 3 other 7300 owners with the same issue, as well as Yaesu and other ICOM models.  Others i have contacted agree that nothing changed in their setup except to upgrade to 2.3.0.  They can all restore the transmitted audio by doing a "halt/enable" cycle.

I appreciate your interest and support - I hope my answers are understandable.

W0RDR