I am also experiencing intermittent transmit audio.  My setup is WSJT-X v2.1.0 and JTAlert v2.15.1, both running on a Win10 PC connected to my TS-590SG through the USB port.  When WSJT-X goes into Tx the rig correctly also switches to Tx mode by CAT control, but there appears to be no audio coming from the PC.  If I'm monitoring the sound out from WSJT-X using Control Panel/Sound when the problem occurs, I see no indication of audio out to the TS-590 USB CODEC.

This only happens occasionally, but always on only the first transmission when trying to initiate a contact.  The second transmission always works.  I have not been able to reproduce this problem on demand.

Any additional thoughts?

Thanks,
Dave, K8WDA