So, I returned the board in question and it was found to have an issue. A replacement was approved and has been received.
Now that I have it in my possession I have uploaded the previous working sketch and connected successfully with the MIT App Inventor app I developed for use as a race start countdown timer interface. Puzzling me now is why the response to the timed signals sent from the phone are now exhibiting a delay in responses on the Thing Plus. For example, I have the sketch set up to flash the RGB LED every second for 5 seconds then light the blue onboard LED for a full second. The sounds emitting from the phone are precisely on time but the response from the board is slower than expected. They used to be perfectly in sync. on the original board. I’m reviewing all the changes to the sketch and app that I might have made to address the Bluetooth communication issue on the 2nd board but not finding where the delay in response from the board relative to the output from the phone is occurring. Any suggestions would be appreciated. I can post code and app blocks as needed later.