Update: I discovered that the 'CP210x USB to UART Bridge' had 'Allow power management' turned on. Unticked the box and Tx audio stays alive during inactivity.
I don't understand how a minor bit of software can drain power.
I'm still getting the 'no Tx audio after band change' problem - new in v2.3.0
I REALLY, REALLY hate Win10.
73 de M0PTB